Key Points GVAX vaccination early after allogeneic HSCT was well tolerated but did not improve long-term disease-free survival after transplantation. This study highlights the challenges of conducting planned early posttransplant intervention trials after allogeneic HSCT.

The ongoing COVID-19 pandemic continues to raise challenges for safe administration of allogeneic hematopoietic stem cell transplantation (allo-HSCT). From March to August 2020, unrelated donor (URD) peripheral blood stem cell (PBSC) products were shipped to central national hubs and cryopreserved either at the site of collection or infusion, a shift from the traditional practice of infusing fresh stem cells. The National Marrow Donor Program (NMDP) instituted this mandate due to uncertainty around international transportation of stem cells as well as a fail-safe to prevent interruptions to a planned transplant if a donor contracted COVID-19 after the recipient started conditioning chemotherapy. We previously published our single institution experience demonstrating equivalent short-term clinical outcomes (overall survival [OS], progression free survival [PFS], relapse, and non-relapse mortality [NRM]) between adult recipients of fresh vs cryopreserved allogeneic stem cells (median follow up time 16 months [fresh] vs 8 months [cryopreserved]) (PMID: 34581754). We also demonstrated lower T-cell chimerism at day 30 and 100 after receipt of cryopreserved grafts. There is a paucity of data evaluating longer term outcomes of patients receiving cryopreserved stem cells compared to fresh. Currently there is variability among donation and transplant centers around the practice of cryopreservation prior to allo-HSCT. With ongoing surges of COVID-19 and evolution of new variants, the risk of donors or recipients contracting COVID-19 leading to delays or disruptions in planned allo-HSCT remains high. In January 2022 with the rise of the Omicron variant of COVID-19, the NMDP reinstated the cryopreservation recommendation. Anecdotal reports indicate multiple recent instances of a planned URD testing positive for COVID-19 after conditioning chemotherapy had started but before stem cell harvest, raising the potential for severe deleterious outcomes in the intended transplant recipient. Given the unremitting COVID-19 surges three years into the pandemic and continued uncertainty around longer-term survival and relapse rates of allo-HSCT using cryopreserved stem cells, we reanalyzed our prior cohort and added 116 additional patients (40 cryopreserved, 76 fresh) with at least 1-year follow up for a total of 141 and 279 patients receiving cryopreserved versus fresh (respectively) URD PBSCs between January 1, 2019, and July 31, 2021. The cohorts had similar baseline characteristics including donor/recipient age/sex, disease, and conditioning regimen/intensity. Patients receiving cryopreserved cells were more likely to receive post-transplant cyclophosphamide as part of the graft versus host disease (GVHD) prophylaxis regimen (24% vs 15%, p=0.015). Median follow-up time among survivors in this cohort was 22 months (range, 4-41 months). Two-year OS was not different in patients receiving fresh versus cryopreserved stem cells (63% vs 63%, p=0.73) (Figure 1A). Two-year PFS was also similar (57% for fresh, 52% for cryopreserved, p=0.27) (Figure 1A). Relapse (36% vs 30%, p=0.17) and NRM (12% vs 13%, p=0.79) at two years were comparable between patients receiving fresh versus cryopreserved stem cells (Figure 1B). In total, 8 patients died of COVID-19 in this cohort (4 fresh, 3 cryopreserved). Cumulative incidence of moderate/severe chronic GVHD (cGVHD) was higher in patients receiving fresh stem cells versus cryopreserved (24% vs 9%, p=0.0003). Whereas cryopreservation was associated with lower T-cell chimerism early after transplant, by 1-year post-transplant, T-cell chimerism was not different (2% vs 5% of fresh vs cryopreserved patients with T-cell chimerism <75% at 1 year, p=0.14). However, Day 30 T-cell chimerism <75% was associated with a reduction in OS and PFS regardless of cryopreservation of stem cells (data not shown). As the COVID-19 pandemic continues with frequent surges in case numbers and rapid viral evolution, the risk for interruptions in life-saving allo-HSCT therapies remains high. Our data show that allo-HSCT with cryopreserved URD PBSCs results in similar OS, PFS, relapse rates, and NRM at 2 years post-transplantation. We found that cryopreservation is associated with lower 1-year cumulative incidence of moderate/severe cGVHD without compromise in OS. While this is an intriguing finding, larger multicenter analyses are needed to confirm these observations. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

CD6 is a co-stimulatory receptor expressed on T cells that binds activated leukocyte cell adhesion molecule (ALCAM), expressed on antigen presenting cells, epithelial and endothelial tissues. The CD6-ALCAM pathway plays an integral role in modulating T-cell activation, proliferation, and trafficking. In this study we examined expression of CD6 by reconstituting T cells in 95 patients after allogeneic cell transplantation and evaluated the effects of itolizumab, an anti- CD6 monoclonal antibody, on T-cell activation. CD6 T cells reconstituted early after transplant with CD4 regulatory T cells (Treg)-expressing lower levels of CD6 compared to conventional CD4 T cells (Tcon) and CD8 T cells. After onset of acute graft-versus-host disease (aGvHD), CD6 expression was further reduced in Treg and CD8 T cells compared to healthy donors, while no difference was observed for Tcon. ALCAM expression was highest in plasmacytoid dendritic cells (pDC), lowest in myeloid dendritic cells (mDC) and intermediate in monocytes and was generally increased after aGvHD onset. Itolizumab inhibited CD4 and CD8 T-cell activation and proliferation in preGvHD samples, but inhibition was less prominent in samples collected after aGvHD onset, especially for CD8 T cells. Functional studies showed that itolizumab did not mediate direct cytolytic activity or antibody-dependent cytotoxicity in vitro. However, itolizumab efficiently abrogated the costimulatory activity of ALCAM on T-cell proliferation, activation and maturation. Our results identify the CD6-ALCAM pathway as a potential target for aGvHD control and a phase I/II study using itolizumab as first line treatment in combination with steroids for patients with aGvHD is currently ongoing (clinicaltrials gov. Identifier: NCT03763318).

We sought to evaluate the impact of cryopreservation of unrelated donor (URD) peripheral blood stem cell (PBSC) grafts on engraftment, chimerism, and immune reconstitution in the context of the COVID-19 pandemic. We reviewed stem cell product characteristics and clinical outcomes in 101 patients receiving cryopreserved PBSCs from URDs between January 1, 2019 and 31 December, 2020, compared with 203 patients receiving fresh URD PBSCs. We observed no differences in 6-month overall survival, progression-free survival, or nonrelapse mortality. Patients receiving cryopreserved PBSCs had delayed platelet engraftment and impaired reconstitution of white blood cells and T-cell subsets at day 30. Thirty-four percent of patients receiving cryopreserved grafts had CD3 chimerism <50% at day 30 after transplantation, compared with 14% of patients receiving fresh PBSCs (P = .0002). At day 100, this difference persisted (CD3+ chimerism <50%: 17% of cryopreserved cohort vs 6% of fresh cohort; P = .016). Greater product age at infusion was associated with increased graft failure, independent of cryopreservation. Receipt of grafts >48 hours old at time of cryopreservation or infusion significantly increased the risk of graft failure (subdistribution hazard ratio = 4.57; 95% confidence interval, 1.71-12.3; P = .0025). Our data indicate that cryopreservation is associated with similar overall short-term clinical outcomes compared with fresh PBSC. However, patients must be monitored closely for increased risk of other potentially adverse outcomes, including graft failure and poor immune recovery, particularly for grafts with older overall age at infusion. Longer-term follow-up is needed to determine impact on relapse and survival.

Background Cytokine-release syndrome (CRS) is a life-threatening complication of haploidentical stem cell transplantation (haploSCT) occurring in the first few days after infusion of the stem cell graft prior to administration of post-transplant cyclophosphamide (PTCY). In the last few years, blockade of IL-6 receptor signaling with tocilizumab has emerged as an effective therapy for Grade 3-4 CRS. As IL-6 mediated signaling is a known regulator of the balance between regulatory T cells (Tregs) and other T cell subsets and has effects on NK cell function, questions remain regarding the effect of the blockade of IL-6 signaling on post-transplant immune cell recovery, engraftment, infection, acute graft-versus-host disease (aGVHD), and the graft-versus-tumor effect. We report on our experience with the use of tocilizumab to treat CRS, and we address the hypothesis that tocilizumab has no effect on the reconstitution of the post-haploSCT myeloid or lymphoid immune subsets. Methods A retrospective review of haploSCT patients with malignacies treated at the Dana-Farber Cancer Institute during the period of 2010-2019 was undertaken. Data included treatment with tocilizumab, cumulative incidence of NRM and relapse, day+30 and day+100 post-transplant chimerism, laboratory markers of viral and fungal infection, and immune reconstitution data at 1-month, 2-month, 3-month, and 6 months post-transplant. Kaplan-Meier analysis of overall survival (OS), including competing risk analysis of the cumulative incidence of relapse and non-relapse mortality (NRM) with the Fine-Gray model was preformed with EZR. Flow cytometry identification of relevant lymphoid populations was performed with a customized panel that included Treg (CD4+CD25+), Tcon (CD4+) and NK (CD3-CD56+) cells. Comparison of the lymphoid populations between the Tocilizumab-treated subgroup of haploSCT patients and the remaining patients was done with the Wilcoxon Mann-Whitney test. Results Out of 132 haploSCT patients, 19 received at least one dose of tocilizumab for the treatment of CRS out of whom one patient died from CRS. In tocilizumab-treated patients myeloid engraftment was 100% at day 30 post transplant. Tocilizumab use was not associated with any effect on lymphoid subset reconstitution at any time point post haploSCT (Figure 1A). Specifically, there was no difference in the reconstitution of NK cells (1-month NK: Mann-Whitney U = 120, p = 0.356; 3-month NK: Mann-Whitney U = 130, p = 0.528; 6-month NK: Mann-Whitney U = 110, p = 0.773), Treg (1-month Treg: Mann-Whitney U = 77, p = 0.412; 3-month Treg: Mann-Whitney U = 104, p = 0.203, 6-month Treg: Mann-Whitney U = 80, p = 0.186), or the Treg:Tcon ratio (1-month Treg:Tcon: Mann-Whitney U = 93, p = 0.835; 3-month Treg:Tcon: Mann-Whitney U = 97, p = 0.141; 6-month Treg:Tcon: Mann-Whitney U = 117, p = 0.959). The 1-year OS in the tocilizumab-treated patient subgroup was 62% (95% CI, 36%-80%) while in the rest it was 76% (95%CI, 67%-83%), with no significant difference between the two subgroups (p = 0.13). The 1-year cumulative incidence of relapse in the tocilizumab-treated subgroup was 19% (95% CI, 4%-42%) while in the rest it was 28% (95% CI, 20%-36%), with no difference between the subgroups (p=0.29). The 1-year NRM in the tocilizumab-treated subgroup was 33% (95% CI, 12%-55%) while in the rest it was 10% (95% CI, 5%-16%), and the difference between subgroups was statistically significant (p = 0.02). Fifty-five percent of patients treated with tocilizumab experienced reactivation of one or more of adenovirus, EBV, CMV or a fungal organism, with 50% of reactivations being CMV and 37% being fungal. Among the tocilizumab-treated patients, 42% experienced any aGVHD with only one patient experiencing Grade 3-4 aGVHD. Conclusions Tocilizumab use is not associated with any effect on post-transplant myeloid engraftment or reconstitution of the Treg, Tcon, and NK cell subsets. Although a significant proportion of tocilizumab-treated patients experienced reactivation of CMV or a fungal organism, the majority of these reactivations were not associated with any clinically significant symptoms. Treatment with tocilizumab was not associated with any significant effect on OS or disease relapse, but the tocilizumab-treated group had a higher NRM than the rest of the haploSCT patients. This association is consistent with prior studies correlating severe CRS with a high NRM, and merits further study. Disclosures Rambaldi: Equillium: Research Funding. Koreth:Amgen: Consultancy; Biolojic Design Inc: Consultancy; Regeneron: Other: Research Support; BMS: Other: Research Support; Cugene: Membership on an entity's Board of Directors or advisory committees; Miltenyi: Other: Research Support; Equillium: Consultancy; Moderna Therapeutics: Consultancy; Therakos: Membership on an entity's Board of Directors or advisory committees; EMD Serono: Consultancy; Clinigen: Other. Cutler:Medsenic: Consultancy, Membership on an entity's Board of Directors or advisory committees; Generon: Consultancy, Membership on an entity's Board of Directors or advisory committees; Mesoblast: Consultancy, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees; Kadmon: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz: Consultancy, Membership on an entity's Board of Directors or advisory committees. Nikiforow:Kite: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Nkarta: Membership on an entity's Board of Directors or advisory committees. Wu:BionTech: Current equity holder in publicly-traded company; Pharmacyclics: Research Funding. Soiffer:Kiadis: Membership on an entity's Board of Directors or advisory committees; Be The Match/National Marrow Donor Program: Membership on an entity's Board of Directors or advisory committees; Celgene: Other; Juno: Other; Novartis: Consultancy; Alexion: Consultancy; VOR Biopharma: Consultancy; Mana Therapeutics: Consultancy; Precision Bioscience: Consultancy; Cugene: Consultancy; Rheos Therapeutics: Consultancy; Gilead: Consultancy. Ritz:TScan Therapeutics: Consultancy; Talaris Therapeutics: Consultancy; Rheos Medicines: Consultancy; Falcon Therapeutics: Consultancy; Avrobio: Consultancy; Kite Pharma: Research Funding; Equillium: Research Funding; Amgen: Research Funding; LifeVault Bio: Consultancy; Infinity Pharmaceuticals: Consultancy.