Efficacy of Third Party BK Virus (BKV) Specific Cytotoxic T-Lymphocytes Generated By Ex Vivo Expansion for the Treatment of BKV Infection in Stem Cell Transplant Recipients, a Phase 2 Trial

Clinical manifestations of BKV hemorrhagic cystits (HC) following hematopoietic stem cell transplantation (HSCT) range from microscopic hematuria to bladder hemorrhage and renal failure. Pharmacologic treatments for HC have limited efficacy and significant adverse effects.

Here, we report the preliminary analysis of adoptive immunotherapy with most closely HLA-matched third party BKV-specific CTL lines (BKV-CTLs) generated by ex vivo expansion.We generated a bank of BKV-specific CTLs from 17 virus-immune healthy donors (mean age, 55; range, 25 to 75 years). Mononuclear cells enriched from donor buffy coats were stimulated with BKV peptide mix from capsid proteins VP1, VP2, VP3, large T antigen (LT) and small T antigen (ST) in the presence of IL-2, IL-7 and IL-15 for 14 days. At the end of culture, the cells were harvested and cryopreserved until use.

Patients with symptomatic BKV cystitis after HSCT for leukemia or lymphoma were eligible. Patients with acute GVHD grades II-IV, those receiving >0.5 mg/kg systemic steroids/day or on treatment with cidofovir or leflunomide were excluded. A search for the most closely HLA-matched donor was initiated through the MDACC cell therapy donor bank. BKV-specific T cells were infused intravenously directly after thawing. Patients could receive up to 2 infusions.

BKV PCR and clinical symptoms were monitored every week for 28 days after infusion. Complete response was defined as complete resolution of symptoms and gross hematuria and partial response (PR) as decrease in grade of HC from 3 (urinary blood clots) or 4 (red cell transfusion requirement/renal impairment) to 2 (macroscopic hematuria) or 3 respectively. Patients with stable disease (SD) or progression had insufficient changes to qualify as PR or had an increase in symptoms or worsening hematuria, respectively.

To date, 10 patients (2 HLA-matched related, 5 HLA-matched unrelated and 3 haploidentical HSCT recipients) have received BKV-CTLs for BK cystitis. The median number of BKV-specific CD3+IFN-gamma+ and CD3+IL-2+ T-cells infused was 10e3/kg and 4.8e3/kg, respectively. The ratio of BKV-specific CD4+/CD8+ T cells in the infused product was 7.8 (range 3.1-22.1). There were no infusion-related adverse effects. Based on end-organ response, BKV-CTLs controlled infection in 9/9 evaluable patients with BKV cystitis (4 CRs and 5 PRs)- one patient was not evaluable due to disease relapse, sepsis and anuria. All patients achieved a response by day 14 post-infusion. Two of 5 patients with PR received a second BK CTL infusion from a different donor. One had an initial PR to the first CTL infusion but symptoms progressed after 6 weeks. A second infusion resulted in a PR with reduction in BKV PCR and symptoms. The other patient achieved CR within 28 days of the second infusion. The time to second infusion was 6 and 3 weeks, respectively. The response in all patients was sustained.

Following infusion, we detected high frequencies of polyfunctional BKV-specific CD4+ and CD8+ T-cells, capable of producing IL-2, IFN-gamma and TNF-alpha in response to ex vivo stimulation with BKV peptide pools (VP1, VP2, VP3, LT and ST). The response was mainly CD4+ T cell dominant, reflecting the composition of the infused BKV T cell line and consistent with previous reports of a predominantly CD4-mediated T cell response in BKV infection.

De novo grade 2-4 acute graft versus host disease (aGVHD) occurred in 1/10 patients. The patient developed grade 2 duodenal GVHD 14 days following infusion. A second patient had recurrence of a prior skin GVHD and developed grade 2 aGVHD 9 days after infusion. Both were successfully treated with 1mg/kg/day systemic steroids.

This analysis demonstrates the safety, feasibility and efficacy of administration of most closely HLA-matched BKV CTLs for the treatment of BKV cystitis in HSCT patients. The response rate of 100% in the first 10 patients treated with BKV CTLs is promising.