Abstract 2165: CD58:CD2 - a multi-dimensional axis in cancer immunotherapy resistance
Authors: Ho Patricia , Melms Johannes , Rogava Meri , Shah Shivem , Izar Benjamin 
Published: June 2022

Abstract
While immune checkpoint blockade therapy has transformed the treatment of metastatic melanoma, most patients exhibit resistance to these therapies, often by unknown mechanisms. We previously found an association of cancer cell autonomous loss of CD58, which encodes a co-stimulatory/adhesion molecule, with immunotherapy resistance in patients. Here, we investigate the mechanistic molecular underpinnings of this observation. In patient-derived melanoma cells co-cultured with autologous tumor infiltrating lymphocytes (TILs), we found that CD58:CD2 ligation is specifically required for TIL-mediated killing and promotes T cell cytokine production. Furthermore, CD58 co-stimulation of TILs enhances their proliferation and activation compared to traditional methods of co-stimulation via CD28. We additionally examined the role of CD58 in vivo. Given that there is no known mouse homolog for CD58, we utilized a humanized mouse model in which hIL-2-expressing NOD/Shi-scid/IL-2Rγnull mice were implanted with patient-derived WT or CD58 knockout (KO) melanoma cells, followed by adoptive cell transfer (ACT) of autologous TILs. We found that CD58 KO tumors were resistant to ACT and had significantly lower TIL infiltration and proliferation compared to WT tumors, and that these effects were rescued by re-expressing CD58. We had previously found that CD58 loss concurrently leads to higher expression of PD-L1, suggesting that enhanced co-inhibitory PD-1/PD-L1 signaling could additionally contribute to cancer immune evasion. To understand CD58/PD-L1 co-regulation, we first sought to delineate genetic and protein-protein regulation of CD58. We performed a genome-wide CRISPR/Cas9 KO screen with FACS enrichment, as well as unbiased CD58 co-immunoprecipitation mass spectrometry screens and identified CMTM6 as a key regulator of CD58. Importantly, CMTM6 was previously identified as a regulator of PD-L1 maintenance, positioning it as a potential candidate for regulating both co-stimulatory (CD58) and co-inhibitory (PD-L1) signals in cancer cells. Indeed, we find that both PD-L1 and CD58 are regulated by CMTM6 at the level of lysosomal degradation. Furthermore, in cells with CD58/CMTM6 double-KO, CMTM6 is required for CD58/PD-L1 co-regulation, which is restored with re-expression of CMTM6. We therefore propose a model in which CD58 regulates PD-L1 by modulating its level of binding to CMTM6; in the absence of CD58, additional CMTM6 is available to bind PD-L1 and thereby stabilize its expression. In summary, we define a central role of the CD58:CD2 axis in tumor immunity and propose that loss of CD58 confers cancer immune evasion through impaired T cell toxicity, tumor infiltration, and concurrent CMTM6-dependent PD-L1 upregulation.
Citation Format: Patricia Ho, Johannes Melms, Meri Rogava, Shivem Shah, Benjamin Izar. CD58:CD2 - a multi-dimensional axis in cancer immunotherapy resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2165.