Microtransplantation: HLA-Mismatched Allogeneic Cellular Therapy of Acute Myeloid Leukemia (HMMACT)
Authors: Mohrbacher Ann , Syed Ibrahim , Merin Noah , Ramsingh Giridharan , Groshen Susan , Chaudhary Preet 
Published: October 2019

Abstract
Background: This clinical trial addressed feasibility and safety of microtransplantation by HLA-mismatched allogeneic cellular therapy (HMMACT) in poor risk acute myeloid leukemia patients. A secondary objective was to estimate complete response rate, infections, GVHD incidence, and induction mortality.
Methods: Patients with high risk AML were enrolled: 4 were > 75 yo, 3 with MLL+ ((t(6;11), 11+ and t(10;11)), 3 complex/del7, one FLT3+. Patients received induction chemotherapy with mitoxantrone (10 mg/m2 IV for 3 days) and cytarabine (150 mg/m2 IV for 7 days) and received HLA-mismatched GCSF mobilized PBSCs on day 9 or 10. Family donors were concurrently HLA typed and best available donor underwent GCSF mobilization (5 mg/kg SQ BID x 4 days) and leukapheresis after medical evaluation and safety testing. HLA partial mismatch patients (4- 5/10 antigen) were chosen. Apheresis cells were counted and analyzed by flow cytometry for CD34+ cells; CD3+, CD4+CD25+ and CD8 + cells; and CD3-CD56+ NK cells. Target CD3 cell dose was 1 x 108/kg per cycle; cells cryopreserved as for standard stem cell donors. Family donor HLA-mismatched GCSF mobilized peripheral blood cells were infused fresh on day 9 or 10 (up to day 16), 36-50 hours after end of cytarabine. Bone marrow biopsy was evaluated on day 14 and 28 for AML remission status, and T/NK cell number. Patients achieving a complete response proceeded to consolidation with cytarabine 0.5 -1.0 gram/m2 x 6 doses with fresh or cryopreserved HMMACT cells from their donor for 2 courses a month apart. Patients: 10 patients age 31 – 80 yo consented: 8 received allo cells; 1 screen failure (no haplo family member identified); 1 patient too ill after initiating chemo to collect donor. Eight patients received at least one course of HMMACT; 1 withdrew early due to AML progression, a second for poor performance status. Three patients had de novo AML; 5 patients had secondary AML. Six Patients had2 or more cycles of HMMACT: four achieved CR: Pt 1 and 4 received 3 cycles, Pt 2 and 6 received 2 cycles of cell infusions and all achieved CR. Pt 9 received 2 inductions with cells, and sustained a partial clinical remission for 6 months. Two Patients had 1 cycle of HMMACT:Pt 3: received 1 cycle cells, but response not assessed; Pt 8: received 1 cycle cells, and achieved CR 3+mos but declined further therapy. Safety: Acute reactions to cell infusions were minimal. Delayed reactions attributed to cell infusions included fever grade 1-2, rash grade 1-2, diarrhea grade 1-2 resolving in 7-10 days. Patients with prior MDS or refractory leukemia requiring 2 inductions had a longer time to ANC and platelet recovery. Feasibility: Two patients had no donor; 2 donors only collected enough for 2 cell infusions. Response: 5/8 pts receiving cells had CR/CRi (62.5%) lasting 3 to 10+ months.
Conclusions: Although there were the usual significant complications of treating leukemia and infections, the cellular therapy itself was well-tolerated. Patients often had fevers in first week after cell infusions, or experienced transient rash and diarrhea in the same time period, which were self resolving in all cases and may reflect elimination of allogeneic cells by the patient’s immune system. No patient developed GVHD. Feasibility of obtaining family donors was as expected for this diverse US population. Infectious complications were low by AML treatment standards. Complete remission rates are encouraging, but not as durable as hoped, likely reflecting the fact that all of our patients had high risk cytogenetics in contrast to the prior published studies by Chinese investigators. The majority were elderly who would not otherwise be offered intensive therapy. Family donors achieved expected cell targets and tolerated mobilization/collection procedures well. All but one patient receiving 2 to 3 cycles achieved complete remission. Two elderly patients who received one or two cell infusions during induction sustained prolonged survival of 6 months in spite of no further therapy, one achieving a CR and the other a sustained PR. Neutrophil and platelet recoveries tended to follow the pattern of the patient's prior secondary leukemia or myelodysplastic disorder. Once patients achieved complete remission however, recovery of blood counts was relatively rapid on further cycles of consolidation. We are now assessing Treg, T and NK cell phenotype of patient and donor cells by flow cyAtometry as biological correlates.

Disclosures
Chaudhary: University of Southern California: Inventor on a patent application relevant to this work filed to US patent office (No. 62/031,053). Patents & Royalties.