Panoply™ Human SIRPA Over-expressing Stable Cell Line

Checkpoint inhibition immunotherapy has revolutionized cancer treatment, but many patients develop resistance. Here, researchers conducted an integrated transcriptomic and proteomic analysis of multiple melanoma clinical cohorts receiving anti-PD-1 therapy, covering both the whole tumor and single-cell levels, aiming to explore emerging immuno-oncology targets. They revealed that tumor-intrinsic SIRPA plays a surprising role in enhancing anti-tumor immunity, a role quite different from its established function as a major inhibitory immunomodulator in macrophages. Loss of SIRPA expression is a hallmark of melanoma dedifferentiation, a key phenotype associated with immunotherapy efficacy. In a co-culture system, inhibition of SIRPA in melanoma cells blocked the killing of tumors by activated CD8+ T cells. Mice carrying SIRPA-deficient melanoma tumors were unresponsive to PD-L1 inhibitor treatment, while melanoma-specific SIRPA overexpression significantly enhanced the immunotherapy response. Mechanistically, SIRPA is regulated by its pseudogene SIRPAP1. These findings suggest that SIRPA plays a complex role in the tumor ecosystem, highlighting the cell type-dependent antagonistic effect of the same target on immunotherapy.

Here, researchers constructed SIRPA knockdown and SIRPA overexpressing stable cell lines (Figure 1D) and demonstrated that SIRPα perturbation in tumor cells had no effect on in vitro tumor growth during co-culture experiments. Compared to the non-targeted control group (NTC), cytotoxic T cells more effectively killed SIRPA-overexpressing tumor cells, while SIRPA-deficient tumor cells were more resistant to T cell-mediated killing (Figure 1E). This indicates that SIRPA plays a positive role in T cell-mediated tumor cytotoxicity on the surface of tumor cells. To further confirm the role of SIRPα in anti-PD-1/PD-L1 therapy, researchers added mouse PD-L1 (mPD-L1) antibody to the co-culture system and observed that the difference in T cell killing effect was more significant than in the control group without antibody (Figure 1E-F). To rule out the possibility that SIRPA perturbation caused altered melanoma differentiation antigen (MDA) expression, researchers analyzed the transcriptomes of SIRPA knockdown and SIRPA overexpression B16F10 cells, finding no significant changes in the expression of six known MDA-encoding genes (PMEL, TYR, TYRP1, DCT, MLANA, and MITF) (Figure 1G). To more directly verify the hypothesis that SIRPA exerts its immunostimulatory effect through CD47-mediated interaction with CD8+ T cells, they used two antibodies, MIAP410 and MIAP430, capable of blocking SIRPα-CD47 interaction, to pretreat T cells before co-culturing and examine whether this blockade affected T cell-mediated cytotoxicity. The results showed that the tumor-killing activity of CD47-blocked T cells was inhibited, while co-culturing with SIRPA-overexpressing melanoma cells enhanced tumor-killing activity (Figure 1H). In summary, these results indicate that melanoma-intrinsic SIRPA can effectively activate the immunogenicity of T cells in PD-1/PD-L1 blockade immunotherapy by interacting with CD47.

Figure 1. Effect of SIRPα inhibition on T cell-mediated antitumor response in melanoma cells. (Zhou Z, et al., 2022)