Background:
We developed a novel biologic (RediTac) to selectively activate and expand virus-specific memory CD8 T cells (CTLs), redirect them to eliminate HIV-infected cells, and thereby eliminate reactivated latent HIV-infected cells. RediTac employs a bispecific Fc-fusion protein scaffold to dimerize HLA-A2 pMHC linked to HIV bNAb scFvs. The pMHC presents a tethered viral peptide for selective binding and stimulation of cognate TCR on virus-specific CTLs, while the scFv redirects the CTL to eliminate HIV-infected cells. As a proof-of-concept, we constructed RediTac with pMHC presenting a CMV-derived peptide, NLV, which is associated with a well-described memory inflation phenotype. The NLV-pMHC was linked to an scFv derived from VRC01, an HIV-1 Env-specific bNAb. This NLV-VRC01 RediTac was tested to determine its ability to redirect CMV-specific CTLs to eliminate HIV-1 Env-expressing cells and suppress HIV-1 infection.
Methods:
Donor PBMC treated with NLV-VRC01 RediTac to expand NLV-specific memory CTLs were cocultured with either an Env-expressing 293T cell line or autologous CD4 T cells infected with an HIV infectious molecular clone expressing a luciferase reporter. NLV-VRC01 RediTac or control treatments were administered and Env-expressing 293T cell killing or luciferase activity reduction was measured as a readout for anti-HIV function.
Results:
Two weeks after NLV-VRC01 RediTac treatment, NLV-specific CTLs expanded by >50-fold compared to untreated controls. Following a two-day coculture, these CTLs eliminated ~40% of Env-expressing 293T cells when treated with fresh NLV-VRC01 RediTac. No elimination was observed when control non-cognate-VRC01 RediTac or NLV-antiCD19 scFv RediTac was added instead. The addition of NLV-VRC01 RediTac without NLV-specific CTLs suppressed HIV infection of donor CD4 T cells by ~35%, indicating neutralizing activity of the VRC01 scFv domain. When NLV-VRC01 RediTac was administered to HIV-infected donor CD4 T cells with syngeneic NLV-specific CTLs, the infection was suppressed by ~70% as compared to untreated cultures.
Conclusions:
NLV-VRC01 RediTac selectively expands CMV-specific memory CTLs and redirects their cytotoxic activity to eliminate HIV-infected cells, and in parallel, also functions as a bNAb to inhibit HIV-1 infection. These results support virus-specific CTL redirection as a novel approach to eliminate latent HIV-infected cells reactivated by LRAs. This approach could contribute to new strategies for a functional HIV-1 cure.
