Optimized Double-Unit Cord Blood Transplantation Mitigates Transplant-Related Mortality Resulting in High Progression-Free Survival in Adults with Hematologic Malignancies

Background : Double-unit cord blood transplantation (dCBT) with intermediate intensity conditioning (Cy50/ Flu150/ Thio10/ TBI400cGy) and cyclosporine-A (CSA)/ mycophenolate mofetil (MMF) graft-versus-host disease (GVHD) prophylaxis has been associated with high progression-free survival (PFS) in adult patients (pts) with hematologic malignancies ( Barker JN et al, Blood Advances 2020). Now, our Center has investigated multiple refinements to further mitigate transplant-related mortality (TRM). Herein, we have analyzed transplant outcomes in these adult dCBT pts to establish an optimized dCBT platform.

Methods : Consecutive adult first allograft pts with high-risk hematologic malignancies who underwent first allografts with intermediate intensity dCBT between 3/2018-8/2022 were analyzed. Optimizations involved further refined unit selection placing highest priority on unit quality (i.e. optimized banking practices) & CD34+ cell dose over HLA-match, ensuring therapeutic (CSA) levels (> 250 ng/mL) by day 0, prompt treatment of pre-engraftment syndrome (PES) & letermovir prophylaxis in CMV seropositive pts from day +7. Also, we have investigated 2 strategies to mitigate acute graft-versus-host disease (aGVHD): pts early in the study period received CSA, MMF & tocilizumab (8 mg/kg on day -1) prophylaxis ( Toci Group), whereas recent pts ( Recent Group) received CSA/ MMF with prompt therapy of clinically diagnosed aGVHD.

Results : Of 74 patients (Table), 49 were in the Toci Group, & 25 in the Recent Group. Most pts were transplanted for acute leukemia (n = 55, 74%) & over half (n = 39, 53%) had non-European ancestry. Distribution of diagnoses, CMV serostatus, HCT-CI & graft characteristics were similar between the groups but Recent Group pts tended to be younger (38 vs. 47 years, p = 0.071).

Toci Group pts had delayed neutrophil recovery [engraftment incidence 94% (95%CI: 87-99) at a median of 25 days (range 16-40), one graft failure], but low rates of PES (n = 19, 39%). The day-100 incidence of grade II-IV & III-IV aGVHD were 69% (95%CI: 56-82) & 10% (95%CI: 2-19), respectively. One pt (false negative CMV-serostatus) who did not receive letermovir had CMV infection. One-year TRM was 16% (95%CI: 6-27) with a 1-year relapse rate of 6% (95%CI: 3-13). TRM was due to infection (n = 3), aGVHD (n = 3, 1 with concurrent COVID-19 infection), multiorgan failure (n = 2) & graft failure (n = 1). With a median follow-up of 47 months (range 28-62), the 1-year OS was 84% (95%CI: 73-94) & 1-year PFS was 78% (95%CI: 66-89).

By contrast, the engraftment incidence in Recent Group pts was 100% with a faster median neutrophil recovery of 19 days (range 11-36, p = 0.002) & all engrafted platelets at a median of 36 days (range 24-92). However, most Recent group pts developed PES [n = 20 (80%), p < 0.001] although this responded promptly to short course corticosteroids. Day 100 grade II-IV aGVHD was also higher [92% (95%CI: 81-99), p = 0.009], although grade III-IV aGVHD was low [8% (95%CI: <1-19)] & similar to tocilizumab pts. Day 100 incidence of CMV was 0%. With a median follow-up of 17 months (range 6-50), the 1-year TRM in Recent Group pts is 0% with a 1-year relapse incidence of 13% (95%CI: 7-27). Consequently, the 1-year OS & PFS are high at 96% (95%: 89-99) & 87% (95%CI: 74-99), respectively (Figure).

Conclusions: Optimized dCBT with intermediate intensity conditioning, graft selection that prioritizes unit quality & CD34+ dose, CSA/ MMF prophylaxis with prompt therapy of PES & aGVHD, & letermovir CMV prophylaxis mitigates TRM in young & middle-aged adults. Thus, combined with relatively low relapse rates, the PFS & OS are high. Tocilizumab has been abandoned due to its notable association with delayed neutrophil engraftment & lack of survival advantage. Letermovir is highly effective completely preventing CMV infections & may contribute to the reduced aGVHD-related mortality recently (as compared to the pre-tocilizumab era), since avoidance of CMV antiviral therapy toxicities greatly facilitates aGVHD prevention & therapy. Given the rapid availability of cryopreserved unmanipulated CB grafts & frequent limitations of URD availability for minority populations, optimized dCBT is a highly attractive curative therapy for acute leukemias & other high-risk myeloid malignancies warranting prospective multi-center investigation.