CD28 is a co-stimulatory molecule expressed on the surface of T cells. To date, three individuals with germline CD28 deficiency have been reported to develop recalcitrant, HPV-driven warts: one exhibited persistent lesions, another experienced disease resolution, and the third developed a chronic "tree-man" phenotype. In mice, we confirmed that CD28-knockout (CD28ko) animals on the C57BL/6 (B6) background are susceptible to cutaneous infection with mouse papillomavirus (MmuPV1); however, their skin warts regressed spontaneously approximately five weeks post-infection. Furthermore, we demonstrate that CD28ko mice are vulnerable to MmuPV1 infection at HPV-relevant mucosal sites, including the most HPV prevalent sites: anogenital tract and oral cavity. Virions recovered from vaginal lavage were infectious but could be neutralized by the neutralizing monoclonal antibody MPV.A4. Viral clearance at mucosal sites was delayed in CD28ko mice, persisting for up to six weeks in the lower genital tract. Blocking the CD28 ligands CD80 and CD86 in B6 mice reproduced the CD28ko phenotype following MmuPV1 infection and markedly reduced CD28 expression, implicating the CD28-CD80/CD86 axis in delayed viral clearance. Infected CD28ko mice showed a reduction in both CD4+ and CD8+ T cell population in the spleen compared to infected B6 mice, but an increase in CD11c+/F4-80+ cells, particularly the plasmacytoid dendritic cell (pDCs, SiglecH⁺) subset. Additionally, CD28ko mice exhibited delayed recruitment of activated CD4+ T cells to infected tissues. Accumulation of MmuPV1 E6/90-99-specific, tetramer-positive CD8+ cytotoxic T lymphocytes (CTLs) was slower in CD28ko than in B6 mice; these CTLs remained FoxP3 negative but displayed reduced efficacy in both in vitro killing and antiviral cytokine assays. Adoptive transfer of CTLs from either B6 or CD28ko mice into MmuPV1-infected Rag1ko mice induced viral clearance at mucosal (oral) sites, whereas B6-derived CTLs achieved more complete regression of cutaneous (tail) lesions. Collectively, these findings indicate that CD28 deficiency delays but does not prevent the clearance of papillomavirus infections at both cutaneous and mucosal sites in mice.

Anti-GD2 immunotherapy has improved survival in children with high-risk neuroblastoma, yet relapse and refractory disease remain major challenges, underscoring the need for strategies that extend therapeutic benefit. We investigated whether inhibition of PIK3C3/VPS34, a class III PtdIns3K that regulates autophagy and endosomal trafficking, could potentiate anti-GD2 therapy. Inducible PIK3C3/VPS34 knockdown induced apoptosis, impaired spheroid growth, and suppressed tumor progression. Notably, PIK3C3/VPS34 depletion enhanced anti-GD2 antibody-driven NK cell cytotoxicity and increased tumor cell-surface GD2 expression. In vivo, combined PIK3C3/VPS34 inhibition and anti-GD2 therapy achieved durable tumor suppression, which was associated with increased infiltration of NK cells and T cells, enhanced T-cell activation, reduced immunosuppressive myeloid populations, enhanced pro-inflammatory macrophage polarization, and elevated production of immune-recruiting chemokines. Pharmacological PIK3C3/VPS34 inhibition recapitulated the effects of genetic depletion, inducing neuroblastoma cell death and enhancing anti-GD2 antibody-dependent NK cell cytotoxicity in vitro. Enhanced NK cell-mediated killing was associated with marked enrichment of GD2 at the tumor cell surface. PIK3C3/VPS34 inhibition caused a disproportionate increase in surface relative to total cellular GD2 levels, while combined inhibition of PIK3C3/VPS34 and lysosomal function resulted in additional GD2 accumulation, supporting a role for endolysosomal processing in controlling GD2 abundance. Together, these findings demonstrate that PIK3C3/VPS34 inhibition enhances the efficacy of anti-GD2 immunotherapy through complementary tumor-intrinsic and immune-mediated mechanisms, including direct tumor cell killing, increased cell-surface GD2 expression, and enhanced antitumor immune responses within the tumor microenvironment, supporting PIK3C3/VPS34 inhibition as a promising therapeutic strategy for high-risk neuroblastoma.Abbreviations: ADCC: antibody-dependent cellular cytotoxicity; ANOVA: analysis of variance; BafA1: bafilomycin A1; dox: doxycycline; ELISA: enzyme-linked immunosorbent assay; FVS780: fixable viability stain 780; FACS: fluorescence-activated cell sorting; GD2: disialoganglioside 2; G-MDSCs: granulocytic myeloid-derived suppressor cells; HCQ: hydroxychloroquine; IP: intraperitoneal; MHC-I: major histocompatibility complex class I; PtdIns3K: class III phosphatidylinositol 3-kinase; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; shRNA: short hairpin RNA; TME: tumor microenvironment; Tregs: regulatory T cells.

The AAA+ ATPase VPS4 drives the ESCRT machinery in diverse intracellular membrane remodeling events, including endocytic receptor sorting, membrane repair, and autophagosome closure. Tumor cells often lose one VPS4 paralog (VPS4A or VPS4B), making them dependent on the remaining enzyme and creating a potential therapeutic vulnerability. Inhibiting VPS4 induces cancer cell-autonomous death and may also modulate the immune microenvironment, although the underlying mechanisms remain unclear. Here, we report that VPS4 inhibition triggered upregulation of cytokine and innate immune signaling, along with canonical NF-κB, stress response, and cell death pathways in murine rhabdomyosarcoma (RMS) cells. Pharmacological and genetic analyses identified the cGAS-STING-TBK1-IRF3 axis, activated by cytoplasmic mitochondrial DNA, as the primary driver of cytokine induction. In an orthotopic syngeneic RMS model, VPS4 inhibition suppressed tumor growth while fostering a more immunogenic microenvironment. Although STING was dispensable for VPS4 inhibition-induced RMS cell death, its loss reduced natural killer and dendritic cell infiltration and attenuated the overall anti-tumor effects of VPS4 inhibition. These findings establish a dual role for VPS4 inhibition in inducing tumor cell death and promoting anti-tumor immunity, highlighting the therapeutic potential of targeting VPS4 vulnerability in cancer.

Melanoma, particularly in its advanced forms, remains one of the most lethal skin cancers, with limited effective treatments for both common cutaneous subtypes and rarer variants such as acral melanoma. The effects of the extracellular matrix (ECM) and other cancer-cell extrinsic processes on melanoma development remain underexplored. This study identifies growth differentiation factor-15 (GDF-15) as a mechanosensing-regulated driver of melanoma pathogenesis across melanoma types. GDF-15 is shown here to be mechanically induced by ECM rigidity and compressive forces occurring during metastatic progression, leading to significantly elevated levels in both cutaneous and acral melanoma cells. In this study, ECM rigidity was recapitulated using cell-adhesive gelatin methacryloyl (GelMA) hydrogel microparticles (microgels) with tunable stiffness, providing a biomimetic platform to investigate how mechanical cues in the tumor microenvironment regulate GDF-15 expression in melanoma. A previously unrecognized synergy between GDF-15 and inflammatory factors commonly present in tumors was identified and found to promote a disorganized, hyperpermeable vasculature, thereby facilitating tumor nutrient access and impeding effective immune cell infiltration. GDF-15 knockdown reduced the intratumoral hemorrhage phenotype, indicating a causal role. GDF-15 also functions by directly suppressing natural killer (NK) cell-mediated cytotoxicity, revealing a second cooperating mechanism of immune evasion. These effects position GDF-15 as a key node linking mechanical stress, co-operation with inflammatory factors, abnormal vascular development, and immune dysfunction, thereby converging on pathways and processes relevant to melanoma progression and treatment.

Melanoma, particularly in its advanced forms, remains one of the most lethal skin cancers, with limited effective treatments for both common cutaneous subtypes and rarer variants such as acral melanoma. The effects of the extracellular matrix (ECM) and other cancer-cell extrinsic processes on melanoma development remain underexplored. This study identifies Growth Differentiation Factor-15 (GDF-15) as a novel mechanosensing-regulated driver of melanoma pathogenesis across melanoma types. GDF-15 is shown here to be mechanically induced by ECM rigidity and compressive forces occurring during metastatic progression, leading to significantly elevated levels in both cutaneous and acral melanoma cells. In this study, ECM rigidity was recapitulated using cell-adhesive gelatin methacryloyl (GelMA) hydrogel microparticles (microgels) with tunable stiffness, providing a biomimetic platform to investigate how mechanical cues in the tumor microenvironment regulate GDF-15 expression in melanoma. A previously unrecognized synergy between GDF-15 and inflammatory factors commonly present in tumors was identified and found to promote a disorganized, hyperpermeable vasculature, thereby facilitating tumor nutrient access and impeding effective immune cell infiltration. GDF-15 knockdown reduced the intratumoral hemorrhage phenotype, indicating a causal role. GDF-15 also functions by directly suppressing natural killer (NK) cell-mediated cytotoxicity, revealing a second cooperating mechanism of immune evasion. These effects position GDF-15 as a key node linking mechanical stress, co-operation with inflammatory factors, abnormal vascular development, and immune dysfunction, thereby converging on a pathways and processes not previously described in melanomas.

Tobacco smoking (TS) is an established etiological factor in the development of head and neck squamous cell carcinoma (HNSCC). We previously developed a mouse model using a select tobacco carcinogen, dibenzo[a,l]pyrene (DB[a,l]P, and its ultimate carcinogenic metabolite diol-epoxide (DB[a,l]PDE) to induce oral squamous cell carcinoma (OSCC) in mice; the molecular characteristics and histological changes observed in the mouse oral cavity mimic those found in human HNSCC. In the present study, using our mouse model, we examined for the first time the co-carcinogenic effects of TS with DB[a,l]PDE on DNA damage, histology, molecular targets, and immune cell regulation. We observed a non-significant increase of the levels of DB[a,l]PDE-DNA adduct in the oral cavity of mice exposed to TS as compared to those exposed to compressed air. Histologically, we observed significant increases in epithelial hyperplasia and epithelial single cell necrosis in TS treated mice. TS significantly enhanced protein expression of NF-κB and Ki67 while the enhancement of COX-2 did not reach significance but p53 expression was significantly decreased. We analyzed immune cell regulation in both spleen and tongue (target organ). No significant changes were observed in the spleen; however, in the tongue, we observed a significantly reduced frequency of CD3+T cells that included reductions of both CD4 and CD8 T cells and a corresponding increase was observed for multiple myeloid cell populations. While preliminary, our results offer the foundation for future research using this mouse model to explore the impact of co-carcinogens/tumor promotors other than TS on critical factors involved in the development of HNSCC.

Programmed cell death protein 1 (PD-1) is expressed by T cells during progressive multifocal leukoencephalopathy (PML), a life-threatening brain disease caused by the human-only JC polyomavirus. Why PD-1 blockade finds variable success in PML patients is unclear. Brain CD4+ and CD8+ T cells are PD-1high during mouse polyomavirus (MuPyV) encephalitis. Here, we show that PD-1 loss during MuPyV infection acts in a brain-autonomous manner to increase the magnitude of brain-infiltrating CD4+ and CD8+ T cells and the function of virus-specific CD8+ T cells; in concert, brain virus levels decline and neuroinflammation increases. Deletion of PD-1 in CD4+ T cells, but not CD8+ T cells, recapitulates effects of global PD-1 loss. Single-cell RNA sequencing shows that PD-1-deficient CD8+ T cells cluster as effectors while transcripts associated with proliferation and function are upregulated with loss of PD-1. Thus, CD4+ T cell-intrinsic PD-1 signaling balances antiviral defense against neural injury during polyomavirus CNS infection.

859 Background: Patients with localized unresectable or cisplatin-ineligible urothelial cancer (UC) have limited treatment options. Biomarker identification can guide targeted therapies. In the DUART study, pre-treatment immune cell subsets were significantly linked to disease control. Our planned correlative aim was to evaluate the same biomarkers using post-adjuvant treatment (post-Rx) peripheral blood mononuclear cells (PBMCs). Methods: This was a prospective, multi-institutional study BTCRC-GU15-023. Our N=16 all had valid Post-Rx values and disease control status. Eligibility criteria: >18yrs, advanced/unresectable UC, and available tumor specimen. All received concurrent durvalumab and radiation therapy followed by adjuvant durvalumab in a Phase II study. Blood samples were taken at pretreatment, 12 weeks, and post-Rx. Biomarkers were detected using multicolor flow cytometry-based analysis of PBMCs to detect T lymphocyte subsets and by dimensionality reduction using FlowJo. Correlative objective: Evaluate post-Rx time points for biomarkers that contribute to disease progression or response. Two-sample T-tests were used to study the association. All tests were two-sided and the statistical significance level used was 0.05. Results: Standard flow cytometry analysis revealed a statistically significant increase in ICOS+ CD4 and CD8 T cells in post-Rx samples among patients with progression-free survival at one year. In addition, responder patients (CR/PR/SD, n=12) showed a significant decrease in CD8 central memory T cells compared to progressors (PD, n=4) in post-Rx samples. Although not statistically significant, additional trends were noted, including decreased PD-1+ CD4 T cells in responder patients, decreased CD4 T effector memory RA+ (TEMRA), and increased CD4 naïve T cells in responder patients. There was a slight increase in interferon gamma-producing CD8 T cell subsets in responder patients and a significant decrease in central memory CD8 T cells. tSNE analysis revealed similar trends in the data, including increased naïve CD4 T cells in responder patients and slight increases in some cytokine-producing CD8 T cell subsets. Conclusions: Our small cohort demonstrates some significant differences in post-Rx T cell populations linked to therapy response, and further evaluation in a larger cohort of patients is needed. The identification of predictive biomarkers could help a more personalized therapeutic approach.

Effective treatment of acute myeloid leukemia (AML) remains an urgent unmet need. Adoptive transfer of cytotoxic T cells (CTLs) against leukemia-associated antigen (LAA) has strong potential to improve AML treatment. However, the clinical translation of this therapeutic modality is hindered by the difficulty of obtaining large quantities of LAA-specific CTLs. Stimulating naïve T cells using monocyte-derived dendritic cells (MoDCs) loaded with LAA is commonly used for the generation of CTLs. This approach has drawbacks as MoDCs loaded with desired antigen need to be developed repeatedly with multiple steps and have limited growth potential. We have established immortalized human dendritic cells (DC) lines (termed ihv-DCs). Here, we report the successful generation of CTLs by culturing AML patient-derived T cells with our off-the-shelf ihv-DCs that carry HLA-A2-restricted human telomerase reverse transcriptase (hTERT), a known LAA. These CTLs exert a potent cytotoxic activity against leukemia cell lines and primary AML blasts in vitro. Importantly, using a highly clinically relevant PDX model where CTLs (derived from clinical donors) were adoptively transferred into NSG mice bearing patient-derived AML cells (that were partial or full HLA match with the donors), we showed that the CTLs effectively reduced leukemia growth in vivo. Our results are highly translational and provide proof of concept using the novel DC methodology to improve the strategy of adoptive T cell transfer for AML treatment.

Acral Lentiginous Melanoma is a rare and aggressive subtype of melanoma that commonly affects the palms, soles, and nail beds. It is more prevalent in individuals with darker skin tones, including Asian, African, and Hispanic populations. Unlike cutaneous melanomas, acral melanoma is not associated with UV exposure and has a distinct genetic and molecular profile, underscoring the need for tailored research and treatment strategies. Standard treatments, such as surgery, chemotherapy, immunotherapy, and targeted therapies, have shown limited success for this melanoma subtype, highlighting the urgency of developing more effective interventions. Telomerase is an enzyme that extends telomeres and is a key target in acral melanoma which exhibits' high telomerase activity, driven by mutations in the telomerase reverse transcriptase TERT promoter, which contributes to uncontrolled tumor cell proliferation, cancer cell immortality, and resistance to conventional therapies. Therefore, targeting telomerase presents a promising therapeutic avenue for acral melanoma patients who do not respond well to current treatments. Several approaches for targeting telomerase deregulation have been developed, and their potential for the management of acral melanoma is discussed in this review. Specifically, the promise of telomerase-targeted therapies for acral melanoma is emphasized and explores how these strategies could improve outcomes for patients with this challenging skin cancer. By focusing on the role of telomerase in tumorigenesis and treatment resistance, telomerase-targeted strategies hold potential as a foundational component of therapies for acral melanoma, complementing existing approaches.

Globally, the incidence of head and neck squamous cell carcinoma (HNSCC) has increased over recent decades and is projected to continue to rise, largely driven by increases in oropharyngeal squamous cell carcinoma (OPSCC), which is linked to HPV infection. HPV infection is also involved in the development of other cancers (anogenital and cervical), and almost 100% of cervical cancer patients are positive for HPV. OPSCC is the most common HPV-associated cancer in men and has exceeded the incidence of cervical cancer cases in women in the USA. Our knowledge of the carcinogenesis process from HPV infection to OPSCC development has been primarily extrapolated from cervical cancer models. While the cooperation of tobacco smoking and HPV infection is documented in cervical cancer, mechanistic studies to address this interaction in management and control of HNSCC are scarce and are also extrapolated from cervical cancer models. The molecular heterogeneity of HNSCC constitutes a tremendous challenge, and despite advances in several fronts in the management and control of HNSCC, short- and long-term treatment-associated morbidities remain substantial. In addition to deaths directly caused by this disease, survivors of this cancer have the second-highest rate of suicide compared with other cancers survivors. Given the existing gaps in our knowledge and the current clinical challenges, future studies including a number of new conceptual and methodological elements discussed in this review can lead to the discovery of biomarkers for early detection of the disease and novel strategies that will advance our knowledge to intercept and prevent HNSCC.

The p53 pathway plays an important role in role in cancer immunity. Mutation or downregulation of the proteins in the p53 pathway are prevalent in many cancers, contributing to tumor progression and immune dysregulation. Recent findings suggest that the activity of p53 within tumor cells, immune cells, and the tumor microenvironment can play an important role in modulating NK cell-mediated immunity. Consequently, efforts to restore p53 pathway activity are being actively pursued to modulate this form of immunity. This review focuses on p53 activity regulating the infiltration and activation of NK cells in the tumor immune microenvironment. Furthermore, the impact of p53 and its regulation of NK cells on immunogenic cell death within solid tumors and the abscopal effect are reviewed. Finally, future avenues for therapeutically restoring p53 activity to improve NK cell-mediated antitumor immunity and optimize the effectiveness of cancer therapies are discussed.

Aldehyde dehydrogenases (ALDHs) are a family of enzymes that aid in detoxification and are overexpressed in several different malignancies. There is a correlation between increased expression of ALDH and a poor prognosis, stemness, and resistance to several drugs. Several ALDH inhibitors have been generated due to the crucial role that ALDH plays in cancer stem cells. All of these inhibitors, however, are either ineffective, very toxic, or have yet to be subjected to rigorous testing on their effectiveness. Although various drug-like compounds targeting ALDH have been reported in the literature, none have made it to routine use in the oncology clinic. As a result, new potent, non-toxic, bioavailable, and therapeutically effective ALDH inhibitors are still needed. In this study, we designed and synthesized potent multi-ALDH isoform inhibitors based on the isatin and indazole pharmacophore. Molecular docking studies and enzymatic tests revealed that among all of the synthesized analogs, compound 3 is the most potent inhibitor of ALDH1A1, ALDH3A1, and ALDH1A3, exhibiting 51.32%, 51.87%, and 36.65% inhibition, respectively. The ALDEFLUOR assay further revealed that compound 3 acts as an ALDH broad spectrum inhibitor at 500 nM. Compound 3 was also the most cytotoxic to cancer cells, with an IC50 in the range of 2.1 to 3.8 µM for ovarian, colon, and pancreatic cancer cells, compared to normal and embryonic kidney cells (IC50 7.1 to 8.7 µM). Mechanistically, compound 3 increased ROS activity due to potent multi-ALDH isoform inhibition, which increased apoptosis. Taken together, this study identified a potent multi-isoform ALDH inhibitor that could be further developed as a cancer therapeutic.

170 Background: The ethanol extract of the root of Angelica gigas Nakai (AGN) dose-dependently inhibits animal models of prostate cancer. Multi-omic analyses have implicated immune and anti-inflammatory responses in the anti-cancer action. In our single dose-PK study (NCT02114957) in healthy volunteers with AGN dietary supplement CognI.Q, we observed a near doubling of the natural killer (NK) mRNA signature in peripheral blood mononuclear cells (PBMC) at 24 h after dosing while the inflammatory cytokine IL-8 mRNA was decreased by one half over the pre-dose baseline. Given NK incapacitation and inflammation have been linked to prostate cancer, the current trial (NCT03630328) was designed to assess safety and to delineate CognI.Q-specific immune and anti-inflammation functions. Methods: We used a double-blinded, placebo-controlled and crossover trial design to monitor hepatic and renal safety metrics based on Comprehensive Metabolic Panel (CMP) and compare the immune cell and cytokine responses to CognI.Q and placebo. Supplement period of 3 weeks was followed with a 2-week washout period. We employed the Ella microfluidic multiplex immunoassay to evaluate select plasma cytokines. Results: Fourteen healthy men completed the trial protocol. Physical examination on study visit days did not reveal any adverse events. Blood CMP monitoring detected abnormal hepatic integrity values in three subjects, all in the second washout period and were attributed to use of anti-allergy medication, an herbal tea for tooth ache, and excessive alcohol, respectively. Analysis of plasma cytokines detected corresponding elevation of MIG, CCL4, CXCL10 and IL-8 with these hepatic damage events. With the exclusion of these subjects or time point, the plasma cytokine measurement did not reveal a significant response to CognI.Q supplement vs. placebo. Conclusions: CognI.Q supplement at the current recommended dose (400 mg, twice per day) did not impair hepatic integrity or renal function, nor did it modulate select plasma cytokines in healthy men. Phase I dose-escalation trials should be implemented to establish safety profile and assess immune and inflammation modulatory effects of AGN supplement beyond the current dose. Clinical trial information: NCT03630328 .

Triple-negative breast cancer (TNBC) is the most aggressive subtype with high metastasis and mortality rates. Given the lack of actionable targets such as ER and HER2, TNBC still remains an unmet therapeutic challenge. Despite harboring high CDK4/6 expression levels, the efficacy of CDK4/6 inhibition in TNBC has been limited due to the emergence of resistance. The resistance to CDK4/6 inhibition is mainly mediated by RB1 inactivation. Since our aim is to overcome resistance to CDK4/6 inhibition, in this study, we primarily used the cell lines that do not express RB1. Following a screening for activated receptor tyrosine kinases (RTKs) upon CDK4/6 inhibition, we identified the TAM (Tyro3, Axl, and MerTK) RTKs as a crucial therapeutic vulnerability in TNBC. We show that targeting the TAM receptors with a novel inhibitor, sitravatinib, significantly sensitizes TNBC to CDK4/6 inhibitors. Upon prolonged HER2 inhibitor treatment, HER2+ breast cancers suppress HER2 expression, physiologically transforming into TNBC-like cells. We further show that the combined treatment is highly effective against drug-resistant HER2+ breast cancer as well. Following quantitative proteomics and RNA-seq data analysis, we extended our study into the immunophenotyping of TNBC. Given the roles of the TAM receptors in promoting the creation of an immunosuppressive tumor microenvironment (TME), we further demonstrate that the combination of CDK4/6 inhibitor abemaciclib and sitravatinib modifies the immune landscape of TNBC to favor immune checkpoint blockade. Overall, our study offers a novel and highly effective combination therapy against TNBC and potentially treatment-resistant HER2+ breast cancer that can be rapidly moved to the clinic.

The goal of this project was to demonstrate that subpopulations of cells in tumors can uniquely fluctuate in size in response to environmental conditions created during drug treatment, thereby acting as a dynamic "rheostat" to create a favorable tumor environment for growth. The cancer modeling used for these studies was subpopulations of melanoma cells existing in cultured and tumor systems that differed in aldehyde dehydrogenase (ALDH) activity. However, similar observations were found in other cancer types in addition to melanoma, making them applicable broadly across cancer. The approach was designed to show that either ALDH(high) and ALDH(low) subpopulations rapidly epigenetically transition between stem-cell-like high into nonstem-like low production states to create an environment during drug treatment that would enable optimal cellular proliferation and tumor expansion to facilitate drug resistance. The controlled experiments showed proportional changes in each cell population to reach an evolutionarily stable equilibrium mediated by the needed levels of ALDH enzyme activity. Mechanistically, cell population size changes served to functionally move the aldehyde and the resulting reactive oxygen species (ROS) levels to those compatible with optimal cellular proliferation with population fluctuations dependent on the levels of drug induced tumor stress. This is the first report documenting fluctuations in the sizes of cell populations in tumors to cooperatively assist in drug resistance development.

Current cancer therapy can be effective, but the development of drug resistant disease is the usual outcome. These drugs can eliminate most of the tumor burden but often fail to eliminate the rare, “Drug Tolerant Persister” (DTP) cell subpopulations in residual tumors, which can be referred to as “Persister” cells. Therefore, novel therapeutic agents specifically targeting or preventing the development of drug-resistant tumors mediated by the remaining persister cells subpopulations are needed. Since approximately ninety percent of cancer-related deaths occur because of the eventual development of drug resistance, identifying, and dissecting the biology of the persister cells is essential for the creation of drugs to target them. While there remains uncertainty surrounding all the markers identifying DTP cells in the literature, this review summarizes the drugs and therapeutic approaches that are available to target the persister cell subpopulations expressing the cellular markers ATP-binding cassette sub-family B member 5 (ABCB5), CD133, CD271, Lysine-specific histone demethylase 5 (KDM5), and aldehyde dehydrogenase (ALDH). Persister cells expressing these markers were selected as the focus of this review because they have been found on cells surviving following drug treatments that promote recurrent drug resistant cancer and are associated with stem cell-like properties, including self-renewal, differentiation, and resistance to therapy. The limitations and obstacles facing the development of agents targeting these DTP cell subpopulations are detailed, with discussion of potential solutions and current research areas needing further exploration.

PDF file - 259K, Supplementary Figure 1. CD8+ T cell accumulation in the TRAMP prostate is tumor antigen-dependent. Supplementary Figure 2. Widespread disease regression in 2X WBI + TCR-IV treated mice. Supplementary Figure 3. Recovery from radiation-induced lymphopenia in TRAMP mice.