DISTINCT EFFICACY AND IMMUNOLOGICAL RESPONSES TO alpha PD-1, alpha PD-L1 AND alpha PD-L2 IMMUNOTHERAPY IN AGED VERSUS YOUNG HOSTS

Background Aging is the biggest risk factor for cancer, yet there are limited pre-clinical/clinical data regarding aging effects on immune checkpoint (IC) inhibition (ICI) outcomes. αPD-1 can potentially block PD-L1 and PD-L2 while αPD-L1 can block PD-1 and CD80. Melanoma response to αPD-1/αPD-L1 correlates with CD8+TCF-1+ T cell stem cell (TCSC) generation.1 Lack of host IL-17 can lead to increased IFN-γ production.2 3 Methods We tested αPD-1 (200 μg/mouse), αPD-L1 (100 μg/mouse) or αPD-L2 (200 μg/mouse) in aged (18–33 months) and young (3–8 months) mice challenged orthotopically with B16 (WT or PD-L1ko) or TPN61R melanoma (NRAS mutation melanoma model)4 (αPD-L2 only) (SQ). Tumors were analyzed by flow. We tested αPD-L2 (20 μg/ml) effects by co-culturing young or aged T cells ± young or aged myeloid cells. Results We reported that αPD-1 treats young and aged with B16 whereas αPD-L1 treats young not aged.5 αPD-L2 treated B16 and TPN61R melanoma in aged but, remarkably, not young, the first single agent anti-cancer immunotherapy exhibiting this property (figure 1). B16 tumors from aged had differential IC content (PD-1, PD-L1, CD80, PD-L2) versus tumors from young (e.g., more PD-L2+ tumor and stroma cells in aged mice; figure 2). Efficacy in young (αPD-1, αPD-L1) and aged (αPD-L2) correlated with increased tumor TCSC content (figure 3). αPD-L2 efficacy against B16 in aged mice required host IFN-γ and IL-17 (figure 4). αPD-1 efficacy against B16 in aged appeared to be host and tumor PD-L1 independent (figure 5). PD-L1KO B16 response to αPD-1 in aged also correlated with increased tumor TCSC content. Myeloid cell PD-L2 signaling inhibited aged but not young CD8+ T cell IL-2 production in vitro (figure 6). Conclusions Treatment differences in aged versus young could depend on IC, TCSC and/or host cytokine differences (IL-17/IFN-γ). αPD-1 efficacy in aged PD-L1KO mice challenged with PD-L1KO B16 suggests that PD-L2 block is sufficient for αPD-1 efficacy in aged. PD-L2 expression differences in the tumor microenvironment could also contribute to treatment efficacy differences. PD-L2 inhibitory signaling on aged but not young CD8+ T cells is a likely mechanism for αPD-L2 efficacy in aged but not young. We are now testing the role of IL-17 in αPD-L2 efficacy as it could be upstream of IFN-γ effects, and TCSC effects in aged versus young. Our work can improve cancer immunotherapy in aged hosts and provides insights into treatment failure, including in young hosts. Acknowledgements South Texas MSTP training grant (NIH T32GM113896), TL1TR002647, NIH T32AI138944, R01 CA231325, Waxman Grant, UL1 TR001120 References Miller BC, Sen DR, Al Abosy R, Bi K, Virkud YV, LaFleur MW, Yates KB, Lako A, Felt K, Naik GS, et al. Subsets of exhausted CD8(+) T cells differentially mediate tumor control and respond to checkpoint blockade. Nat Immunol 2019;20(3):326–336. Moroda M, Takamoto M, Iwakura Y, Nakayama J, Aosai F. Interleukin-17A-deficient mice are highly susceptible to toxoplasma gondii infection due to excessively induced T. gondii HSP70 and interferon gamma production. Infection and immunity 2017;85(12):e00399–00317. Yi T, Zhao D, Lin C-L, Zhang C, Chen Y, Todorov I, LeBon T, Kandeel F, Forman S, Zeng D. Absence of donor Th17 leads to augmented Th1 differentiation and exacerbated acute graft-versus-host disease. Blood, The Journal of the American Society of Hematology 2008;112(5):2101–2110. Burd CE, Liu W, Huynh MV, Waqas MA, Gillahan JE, Clark KS, Fu K, Martin BL, Jeck WR, Souroullas GP. Mutation-specific RAS oncogenicity explains NRAS codon 61 selection in melanoma. Cancer discovery 2014;4(12):1418–1429. Padron A, Hurez V, Gupta HB, Clark CA, Pandeswara SL, Yuan B, Svatek RS, Turk MJ, Drerup JM, Li R, et al. Age effects of distinct immune checkpoint blockade treatments in a mouse melanoma model. Exp Gerontol 2018;105:146–154. Ethics Approval All animal studies are approved by UTHSA IACUC.