Cellular and Molecular Dissection of the CD8+ T-Cell Response to Kaposi Sarcoma: Implications for Immunotherapeutic Strategies

Abstract

Kaposi sarcoma-associated herpesvirus (KSHV) is one of two known tumorigenic human herpesviruses and the etiologic agent of Kaposi sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman disease (MCD), malignancies that predominantly arise in the context of T-cell deficiency or dysfunction. There are no approved vaccines, antiviral drugs, or immunotherapies that can prevent or eliminate KSHV infection. The impact of this therapeutic gap is most pronounced in sub-Saharan Africa (SSA), where the burden of KS morbidity and mortality is highest, KSHV is endemic, and HIV-1, the greatest risk factor for KS, is highly prevalent. All other human herpesviruses elicit potent and durable antiviral T-cell responses to control infection. However, studies of circulating T-cell responses to KSHV in the blood suggest that this response is heterogeneous, infrequent, and low-intensity, with the identity of their peptide-MHC targets poorly defined. Given the consistent expression of KSHV in KS tumors, we hypothesized that KSHV-specific T cells would be frequently recruited to KS tumors. We therefore analyzed the TCR repertoire of tumor biopsies from 144 Ugandan adults with KS, 106 of whom were people living with HIV (PLWH). Clusters of T cells with predicted shared specificity for uncharacterized antigens comprised approximately 25% of the T-cell repertoire in the KS tumor microenvironment, representing 4,283 unique αβ TCRs potentially recognizing KSHV- or HIV-encoded peptide antigens. From 25 reconstructed TCRs, we identified two ORF6-specific, HLA-B*45:01-restricted TCRs, one HLA-B*57:03-restricted TCR with specificity for ORF59, and one HLA-A*66:01-restricted TCR recognizing ORF57. The ORF6- and ORF59-specific TCRs were detected in 27-29 and 30 tumors from 14 HLA-B*45:01+ and 10 HLA-B*57:03+ individuals, respectively. Therefore, these TCRs provide the first evidence of a shared, i.e., “public,” T-cell response to KSHV. Primary CD8+ T cells engineered with KSHV-specific TCRs from KS tumor-infiltrating lymphocytes displayed high-avidity, MHC-restricted recognition of two distinct cell types infected with KSHV, B cells (PEL) and endothelial cells (iTIME.219). In parallel, we characterized three novel HIV-specific TCRs within KS tumors from PLWH, two targeting Nef71-79 and one recognizing Vpr34-42, and confirmed the presence of a previously described public HIV-specific TCR recognizing Pol982-990. HIV-specific T cells remained detectable in KS tumors from individuals who had been on antiretroviral therapy for up to five months. Together, these findings demonstrate that KS tumors recruit polyclonal, high-avidity CD8+ T cells recognizing multiple lytic KSHV and in PLWH, HIV antigens. The identification of CD8+ T cells capable of killing diverse KSHV-infected cell types will provide the foundation for rational vaccine design and TCR-based immunotherapeutic strategies to prevent or treat KS.