Administration of Most Closely HLA-Matched Multivirus-Specific T Cells for the Treatment of EBV, CMV, AdV, HHV6, and BKV Post Allogeneic Hematopoietic Stem Cell Transplant

Viral infections remain a significant cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (HSCT). Adoptive immunotherapy with donor-derived virus-specific T cells (VSTs) has proven safe and effective for the prophylaxis and treatment of EBV, CMV, AdV, BKV and HHV-6 infections post-HSCT. However, broader application is restricted by the time taken to prepare patient-specific products and the lack of virus-specific T cell precursors in cord blood and seronegative donors. Thus, to assess whether 3^rd party multivirus-directed VSTs could produce clinical benefit when administered as an "off the shelf" product to partially HLA-matched allogeneic HSCT recipients with drug-refractory BKV, EBV, CMV, AdV and/or HHV-6 infections we initiated a Phase II clinical trial (fixed cell dose of 2x10⁷ VSTs/m²) using a bank of 59 VST lines generated from healthy, eligible donors.

To date, 32 patients with one (n=28) or two (n=4) drug-refractory infections have been infused with lines matched at 1 to 6 HLA antigens. Fifteen patients received VSTs to treat CMV (including 3 cases of CMV colitis), 13 for BKV (11 for hemorrhagic cystitis, 2 for nephritis), 4 for AdV (including 1 case of pneumonia), 2 for HHV-6 (including 1 case of encephalitis) and 2 for EBV (including 1 case of EBV-PTLD). Twenty-one patients received just 1 infusion of cells, while 11 required 2 or 3 infusions for sustained benefit. Despite the HLA disparity between the VST lines and the recipients, de novo graft versus host disease (GVHD) occurred in only 1 subject, who developed Grade I skin GVHD that resolved with topical steroids. One additional patient had a flare of chronic skin GVHD coincident with tapering of immunosuppression and 2 patients developed transient fevers a few hours post-infusion, which spontaneously resolved within a couple of hours.

Based on viral load, as measured by quantitative PCR, 3^rd party VSTs successfully controlled active infections in 29 of 31 evaluable patients: CMV (9 CR, 5 PR, 1 NR); EBV (2 CR); AdV (2 CR, 1 PR, 1 NR); BKV (4 CR, 9 PR); and HHV-6 (1 PR). Of note, all 11 patients with BK hemorrhagic cystitis, 2 of 3 patients with CMV colitis, and the patients with AdV pneumonia and HHV-6 encephalitis, all had marked improvement or resolution of symptoms within 6 weeks following VST treatment. In more than 50% of responders (n=16) we detected an increase in the circulating frequency of VSTs post-infusion, which were confirmed to be 3^rd party VST origin in 8 and remained detectable for up to 12 weeks post-infusion. The eventual decrease in 3^rd party VSTs coincided with endogenous immune reconstitution in most patients.

These results confirm the feasibility and safety of 3^rd party multivirus-directed VSTs, administered as an "off the shelf" product to treat drug-refractory infections/disease. The infused cells were capable of expanding in vivo and proved clinically effective against refractory EBV, CMV, AdV, BKV and HHV-6 reactivation and virus associated disease.