T-cell receptor/CD28-targeted immunotherapeutics selectively drive naive T-cell expansion to generate functional HIV-specific responses

Adoptive cell transfer (ACT), a promising immunotherapeutic approach, treats viral infections or cancer by ex vivo expansion and infusion of antigen-specific CD8+ T cells, respectively. However, its wider use is limited by logistical challenges associated with the conventional method of using patient-derived dendritic cells (DCs) loaded with peptides for ex vivo antigen-specific CD8+ T cell expansion. To overcome these limitations, we developed Immuno-STAT (IST), a dimeric protein scaffold that delivers peptide-specific T cell receptor (TCR) activation with or without CD28 costimulatory signals to expand CD8+ T cells specific for defined viral or cancer epitopes. In this proof-of-concept study, we demonstrate that anti-CD28-IST can selectively activate and expand polyfunctional cytotoxic CD8+ T cells from the naive repertoire, targeting the HIV-associated SL9 or melanoma-associated MART-1 epitopes. Naive MART-1-specific CD8+ T cells were reliably expanded by both peptide-loaded DCs and IST. In contrast, naive SL9-specific CD8+ T cells were expanded only by SL9-specific IST and not by conventional DC-based approaches, underscoring a unique ability of IST to stimulate some naive HIV-specific T cell responses. IST-derived SL9-specific CD8+ T cells exhibited potent cytotoxicity, diverse TCR clonotypes, and memory-differentiated phenotypes, marking a significant advance in generating antigen-specific T cells against HIV. The modular IST platform provides a scalable modality to stimulate naive CD8+ T cells to potentially mobilize preemptive CD8+ T cell responses against predicted immune escape variants, as well as subdominant conserved HIV epitopes to empower the development of innovative ACT, vaccine, and other immune strategies to advance treatments for HIV, other persistent viral infections, and cancer.