Investigators evaluated the clinical utility of Multivirus VSTs in recipients of matched related, matched unrelated, or haploidentical donor transplants. To date, 10 clinical-grade multivirus-directed VSTs have been generated from donor PBMCs. These lines were polyclonal, comprising both CD4+ (57±5%) and CD8+ (35±5%) cells and retained expression of the memory markers CD45RO+CD62L+ (58±8%). Their specificity was dependent on the prior viral exposure of the cell donor; 7/8 tested lines had activity against Adv,8/8 against CMV, 6/8 against EBV. None of the lines reacted against recipient PHA blasts - indicating lack of alloreactive potential in these rapidly generated lines.

Investigators administered these multivirus-specific donor-derived VSTs to 3 allogeneic HSCT recipients in a dose escalation study all on DL1 (5x106/m2). There were no immediate infusion toxicities, and no de novo acute GvHD, demonstrating the in vivo safety of these mVST. Further, antiviral efficacy has been observed in 1 patient with refractory CMV. In addition, in a recently published paper from Baylor College of Medicien (Anapoulous et al, STM 2014) they have treated VSTs manufactured with a similar methodology, but targeting 5 viruses instead of 3 with specificity to BK virus and HHV6. In that study 10 patients were treated with 4 on DL1 (5x10e6/m2), 4 on DL2 (1x10e7/m2) and 2 on DL3 (2x10e7/m2) and again saw no immediate infusion toxicities, and no de novo acute GvHD, demonstrating the in vivo safety of these mVST. Three patients received the cells as viral prophylaxis (days 38-43 post-HSCT) and none developed viral infections at up to 3 months post-treatment. The other 7 patients received the cells as treatment for one or more active infections between days 59-139 post-HSCT. Based on viral load measurements by day 42 post-infusion, the VSTs were successful in controlling active infections with CMV (1 complete (CR) and 1 partial response (PR)), EBV (2 CRs, including a case of frank PTLD); Adv (1 CR); HHV6 (1 CR); and BK (3 CR, 1 PR, 1NR). Of note, 3 BK virus responders had tissue disease with severe hemorrhagic cystitis and all had marked improvement or disappearance of hematuria following infusion. One patient subsequently had an episode of transient but severe bladder pain in association with inflammation seen on cytoscopy coincident with a 6 log fall in urine BK viral load. Only non-responder was a patient with BK infection whose line lacked activity for this virus, likely reflecting the serostatus of the donor. In addition, 3 patients subsequently reactivated other viruses than those for which they were initially treated, but all cleared these infections by week 12, without the requirement for additional cell infusions (CMV: 1CR; EBV: 1CR; BK: 1CR; HHV6: 1CR). Finally, 1 patient received multivirus specific VSTs under a single patient protocol as an emergency treatment for widespread and bulky rituximab-resistant EBV-PTLD. Post VST treatment there was an immediate decline in the patient's EBV viral load with complete and sustained resolution of PTLD, coincident with an increase in circulating EBV-specific T cells. However, the profound anti-tumor activity mediated by the rapidly-expanding EBV-directed T cells also produced a transient systemic inflammatory response syndrome, which was controlled with steroids and anti-TNFR antibody, with no long term adverse effects.

Thus, infusion of donor-derived, multivirus specific VSTs generated with clinical grade pepmixes and infused either prophylactically or as treatment for one or more viral infections has been safe and is associated with the appearance of virus-reactive T cells in peripheral blood that have been able to control infection with above mentioned viruses.