Treatment Of Steroid-Refractory Acute GVHD With Mesenchymal Stem Cells Improves Outcomes In Pediatric Patients; Results Of The Pediatric Subset In A Phase III Randomized, Placebo-Controlled Study

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long term outcomes of pediatric patients with malignant and non malignant disorders receiving α β t cell depleted hla haploidentical hematopoietic stem cell transplantation hsct followed by infusion of bpx 501 t cells donor t cells transduced with ic9

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Allogeneic Human Mesenchymal Stem Cell Therapy (Remestemcel-L, Prochymal) as a Rescue Agent for Severe Refractory Acute Graft-versus-Host Disease in Pediatric Patients

AbstractSevere steroid-refractory acute graft-versus-host disease (aGVHD) is related to significant mortality and morbidity after allogeneic stem cell transplantation. Early clinical trials of therapy with human mesenchymal stem cells (hMSCs) in pediatric patients with severe aGVHD resistant to multiple immunosuppressive agents showed promising results. In this study, we evaluated the risk/benefit profile of remestemcel-L (Prochymal), a third-party, off-the-shelf source of hMSCs, as a rescue agent for treatment-resistant aGVHD in pediatric patients. Children with grade B-D aGVHD failing steroids and, in most cases, other immunosuppressive agents were eligible for enrollment. Patients received 8 biweekly i.v. infusions of 2 × 106 hMSCs/kg for 4 weeks, with an additional 4 weekly infusions after day +28 for patients who achieved either a partial or mixed response. The enrolled patients compose a very challenging population with severe disease that was nonresponsive to the standard of care, with 88% of the patients experiencing severe aGVHD (grade C or D). Seventy-five patients (median age, 8 yr; 58.7% male; and 61.3% Caucasian) were treated in this study. Sixty-four patients (85.3%) had received an unrelated hematopoietic stem cell graft, and 28 patients (37.3%) had received a cord blood graft. At baseline, the distribution of aGVHD grades B, C, and D was 12.0%, 28.0%, and 60.0%, respectively. The median duration of aGVHD before enrollment was 30 d (range, 2 to 1639 d), and patients failed a median of 3 immunosuppressive agents. Organ involvement at baseline was 86.7% gastrointestinal, 54.7% skin, and 36.0% liver. Thirty-six patients (48.0%) had 2 organs involved, and 11 patients (14.7%) had all 3 organs involved. When stratified by aGVHD grade at baseline, the rate of overall response (complete and partial response) at day +28 was 66.7% for aGVHD grade B, 76.2% for grade C, and 53.3% for grade D. Overall response for individual organs at day +28 was 58.5% for the gastrointestinal system, 75.6% for skin, and 44.4% for liver. Collectively, overall response at day +28 for patients treated for severe refractory aGVHD was 61.3%, and this response was correlated with statistically significant improved survival at day +100 after hMSC infusion. Patients who responded to therapy by day +28 had a higher Kaplan-Meier estimated probability of 100-d survival compared with patients who did not respond (78.1% versus 31.0%; P < .001). Prochymal infusions were generally well tolerated, with no evidence of ectopic tissue formation

Administration of BPX-501 Cells Following Αβ T and B-Cell-Depleted HLA Haploidentical HSCT (haplo-HSCT) in Children with Acute Leukemias (AL)

Background Allogeneic HSCT is a well-established treatment for children with AL. For pts lacking a compatible matched related or unrelated donor, HLA-haplo-HSCT represents an alternative. Promising results were reported with selective depletion of αβ T and B cells (Locatelli, Blood 2017). PX-501 is an allogeneic product consisting of T cells modified to express the inducible caspase-9 (iC9) safety switch and truncated CD19 to allow monitoring and expansion of BPX-501 following transplant. BPX-501 provides broad virus and tumor-specific immunity; the safety switch provides the unique ability to promptly and durably resolve graft-versus-host disease (GvHD) symptoms following the administration of rimiducid. Aims Evaluate the safety and efficacy of BPX-501 in pediatric pts with AL by determining whether BPX-501 infusion can increase efficacy outcomes through an enhanced graft-versus-leukemic (GvL) effect, while maintaining a low risk of GvHD. Methods A subset of pts had high-risk ALs. BPX-501 was planned to be infused on day14±4 after the allograft with no post-transplant GvHD prophylaxis allowed. Pts who developed steroid-resistant GvHD could receive ≥1 dose of rimiducid. Results As of June 30, 2018, 100 pts with AL (described in Table 1) were efficacy evaluable. Median time for neutrophil and platelet engraftment was 16 and 12 days, respectively. Four pts (4.1%) experienced primary graft failure. Of 96 evaluable pts, 5 (3.1%) developed Grade III-IV aGvHD. Of 82 evaluable pts, 12 developed cGvHD (18.1%), with 3 moderate-severe. Rimiducid was administered to 10 pts. Best overall clinical response (CR/PR) post-rimiducid was 80% (8 pts). Among responding patients, 7 (87.5%) had a CR. Six (6.6%) pts died after transplantation. Efficacy outcomes in AL subsets are in Table 2. CD3+ and CD3+CD4+ T cells above 500 cells/ml were achieved by 180 and 270 days, respectively. IgA and IgM levels achieved normal values by 180 days. Conclusion BPX-501 following αβ-T and B-cell depleted haplo-HSCT represents a highly effective transplantation strategy for pediatric pts with AL. Rimiducid was an effective treatment for pts with steroid-resistant GvHD

Conditioning with Treosulfan and Fludarabine followed by Allogeneic Hematopoietic Cell Transplantation for High-Risk Hematologic Malignancies

In this prospective study 60 patients of median age 46 (range: 5-60 years), with acute myelogenous leukemia (AML; n = 44), acute lymphoblastic leukemia (ALL; n = 3), or myelodysplastic syndrome (MDS; n = 13) were conditioned for allogeneic hematopoietic cell transplantation with a treosulfan/fludarabine (Flu) combination. Most patients were considered at high risk for relapse or nonrelapse mortality (NRM). Patients received intravenous treosulfan, 12 g/m2/day (n = 5) or 14 g/m2/day (n = 55) on days −6 to −4, and Flu (30 mg/m2/day) on days −6 to −2, followed by infusion of marrow (n = 7) or peripheral blood stem cells (n = 53) from HLA-identical siblings (n = 30) or unrelated donors (n = 30). All patients engrafted. NRM was 5% at day 100, and 8% at 2 years. With a median follow-up of 22 months, the 2-year relapse-free survival (RFS) for all patients was 58% and 88% for patients without high-risk cytogenetics. The 2-year cumulative incidence of relapse was 33% (15% for patients with MDS, 34% for AML in first remission, 50% for AML or ALL beyond first remission and 63% for AML in refractory relapse). Thus, a treosulfan/Flu regimen was well tolerated and yielded encouraging survival and disease control with minimal NRM. Further trials are warranted to compare treosulfan/Flu to other widely used regimens, and to study the impact of using this regimen in more narrowly defined groups of patients

Transplantation Outcomes for Children with Hypodiploid Acute Lymphoblastic Leukemia

Children with hypodiploid acute lymphoblastic leukemia (ALL) have inferior outcomes despite intensive risk adapted chemotherapy regimens. We describe 78 children with hypodiploid ALL who underwent hematopoietic stem cell transplant (HSCT) between 1990 and 2010. Thirty nine (50%) patients had ≤ 43 chromosomes, 12 (15%) had 44 chromosomes and 27 (35%) had 45 chromosomes. Forty three (55%) patients were transplanted in first remission (CR1) while 35 (45%) were transplanted in ≥CR2. Twenty nine patients (37%) received a graft from a related donor and 49 (63%) from an unrelated donor. All patients received a myeloablative conditioning regimen. The 5-year probabilities of leukemia-free survival (LFS), overall survival (OS), relapse, and treatment related mortality (TRM) for the entire cohort were 51%, 56%, 27% and 22% respectively. Multivariate analysis confirmed that mortality risks were higher for patients transplanted in CR2 (HR 2.16, p=0.05), with chromosome number ≤43 (HR 2.15, p=0.05) and for those transplanted in the first decade of the study period (HR 2.60, p=0.01). Similarly, treatment failure risks were higher with chromosome number ≤43 (HR 2.28, p=0.04) and the earlier transplant period (HR 2.51, p=0.01). Although survival is better with advances in donor selection and supportive care, disease-related risk factors significantly influence transplantation outcomes

The genomic landscape of juvenile myelomonocytic leukemia

Juvenile myelomonocytic leukemia (JMML) is a myeloproliferative neoplasm (MPN) of childhood with a poor prognosis. Mutations in NF1, NRAS, KRAS, PTPN11 and CBL occur in 85% of patients, yet there are currently no risk stratification algorithms capable of predicting which patients will be refractory to conventional treatment and therefore be candidates for experimental therapies. In addition, there have been few other molecular pathways identified aside from the Ras/MAPK pathway to serve as the basis for such novel therapeutic strategies. We therefore sought to genomically characterize serial samples from patients at diagnosis through relapse and transformation to acute myeloid leukemia in order to expand our knowledge of the mutational spectrum in JMML. We identified recurrent mutations in genes involved in signal transduction, gene splicing, the polycomb repressive complex 2 (PRC2) and transcription. Importantly, the number of somatic alterations present at diagnosis appears to be the major determinant of outcome

Anti-CD45 Pretargeted Radioimmunotherapy in a Nonhuman Primate Model.

The efficacy of radiolabeled antibody (RAb) therapy has been validated by high response rates in hematologic malignancy, yet patients treated with conventional non-myeloablative doses of radioimmunotherapy (RIT) usually relapse. Low tumor-to-normal organ ratios of absorbed radioactivity are the result of ongoing non-specific radiation exposure through the circulation; this accumulates over time and is dose limiting. Our group has documented the efficacy of pretargeted RIT in murine models, using an anti-human (h)CD45 antibody (BC8). We have engineered, expressed, and purified a recombinant tetravalent single chain antibody (Ab)-streptavidin fusion protein [(scFv) 4 -SA] directed against (h)CD45. The tetrameric fusion protein (FP) retains the full antigen binding capacity of intact Ab. Because the tumor-reactive FP is not bound to a therapeutic radionuclide, it can localize to tumor sites without subjecting the rest of the body to non-specific irradiation. After maximal accumulation of BC8-FP in the tumor, a small molecular weight radioactive moiety with high affinity for the tumor-reactive FP is administered (radio-DOTA-biotin). This second reagent penetrates tumors rapidly where it binds to the pretargeted FP. Unbound radio-DOTA-biotin molecules are small enough to be rapidly cleared from the blood and excreted in the urine within minutes. In a series of studies involving fourteen fascicularis Macaques, we have shown that this two-step pretargeting approach using BC8-FP is feasible, safe and effective. We have identified that the blood clearance kinetics of radiolabeled BC8-FP are comparable to conventionally radiolabeled intact Abs (t 1/2 = 40.6 and 50.2 hrs respectively), and have determined that the optimal time-point for radio-DOTA-biotin administration is 48 hrs after FP infusion. We found BC8-FP uptake in target tissue (lymph node and spleen) to be very specific when compared with a control anti-TAG72 (scFv) 4 -SA (CC49-FP). Measured on a gamma counter at 96 hrs post infusion, the percent injected dose per gram (%ID/g) was 0.28±0.01 for BC8-FP and 0.03±0.01 for CC49-FP in lymph nodes (LN); and 0.33±0.02 and 0.07±0.002, respectively, in spleen. Serial LN biopsies and terminal spleen tissue harvests in animals co-injected with equimolar concentrations of intact BC8 antibody and BC8-FP, revealed equivalent initial uptake in target tissue, but superior retention of BC8-FP over time. After 96 hrs, the %ID/g of 111 In-BC8-FP in lymph node was 0.93±0.02, compared to 0.046±0.013 for BC8 Ab. In spleen the %ID/g was 0.158±0.0 for BC8-FP versus 0.057±0.0 for BC8 Ab. With two-step pretargeting, LN-to-blood and spleen-to-blood ratios 48 hours after 111 In-DOTA-biotin were 10.3:1 and 13.9:1, respectively, while for conventional BC8 Ab they were 2.6:1 and 3.0:1 respectively. These studies demonstrate that multi-step pretargeting can improve tumor-to-normal organ ratios of radionuclide delivery in a nonhuman primate model and offer the promise of more durable responses in patients with hematologic malignancy. Further investigation of radiolabeled BC8 as a rational therapeutic agent for both myeloid leukemia and non-Hodgkin’s lymphoma is warranted. Additional studies are planned involving introduction of a dendrimeric N-acetyl galactosamine “clearing agent” to further improve the therapeutic index. Future patient clinical trials are anticipated