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.

Importance: Adoptive transfer of ex vivo-expanded T cells with potent and broad anti-HIV activity may control HIV replication in people with HIV in the absence of antiretroviral therapy. To selectively activate and expand naive CD8+ cells targeting defined viral or cancer epitopes, we developed a unique protein architecture, termed Immuno-STAT, which delivers cognate peptide-specific T cell receptor (TCR) activation alone or in combination with CD28 costimulation. We demonstrated that polyfunctional cytotoxic CD8+ T cells specific for the HIV-associated SL9 or melanoma-associated MART-1 epitopes were expanded by αCD28-Immuno-STAT delivering peptide-specific TCR and CD28 signals, but not peptide-specific TCR signals alone. αCD28-Immuno-STAT-generated SL9-specific CD8+ T cells exhibited diverse TCR clonotypes, polyfunctionality, and potent SL9-specific cytotoxicity. Adoptive transfer of αCD28-Immuno-STAT-generated CD8+ T cells specific for defined HIV epitopes may provide the broad yet targeted responses specific for conserved HIV epitopes and predicted immune escape variants required to control HIV replication and provide a functional HIV cure.