Treatment of Bleeding in Severely Thrombocytopenic Patients with Transfusion of Dimethyl Sulfoxide (DMSO) Cryopreserved Platelets (CPP) Is Safe - Report of a Phase 1 Dose Escalation Safety Trial

Availability of platelets (plts) is severely limited by shelf life in some military as well as civilian settings. Additionally, some bleeding, thrombocytopenic patients do not have a therapeutic response to a standard plt transfusion. Methods for cryopreservation of apheresis plts for up to two years in 6% DMSO at <-65°C (CPP) have been developed and evaluated by in vitro assays and by in vivo infusions in non-human primates, in a few controlled human trials, and in field military operations. However, FDA has not yet approved CPP for routine use. Autologous radiolabeled CPP in healthy volunteers (n=32) had average plt recoveries of 33 ± 10% and survivals of 7.5 ± 1.2 days, and these results were 52 ± 12% and 89 ± 15%, respectively, of the same volunteers' fresh radiolabeled plts. The in vitro phenotype of CPP showed higher granule secretion, phosphotidylserine expression, and plt microparticles and poorer responses to common plt agonists compared to standard room temperature stored plts. These data suggest that transfused CPP might lead to an accelerated and enhanced clotting process in vivo. Our objective was to evaluate the safety of transfused CPP in a Phase-1 dose escalation trial.

Eligibility criteria were hospitalized thrombocytopenic hematology/oncology patients with active World Health Organization (WHO) Grade 2 or greater bleeding that was, in most patients, uncontrolled by standard plts, no history of unprovoked thrombotic events, and no indication of active DIC. Fifty-nine patients consented and 28 were transfused with ½ CPP unit (n=5), one CPP unit (n=7), two CPP units (n=6), and three CPP units (n=6). One thawed single apheresis CPP unit contained 2.5 x 10¹¹ ± 4.2 x 10¹⁰ plts in 50 ± 4 ml. In addition, one standard apheresis plt unit was randomly given to patients enrolled in each cohort (n=4). The study conformed to the Declaration of Helsinki and was listed on clinical trials.gov (NCT02078284). Patients were monitored for six days post-transfusion for adverse events (AEs) including clinical assessments for signs or symptoms of thrombosis and specific laboratory assays: prothrombin time (PT), partial thromboplastin time (aPTT), D-dimer, fibrinogen, prothrombin fragments 1 + 2 (F1+2), antithrombin, thrombin antithrombin (TAT), thrombin generation (TGT), and thromboelastography (TEG). All safety data were reviewed by an independent data safety monitoring committee prior to escalation to the next higher dose cohort.

No thrombotic events occurred after transfusion of CPP units. Five serious AEs were reported, and none were associated with the CPP transfusion but, rather, were related to worsening of the patients' underlying medical conditions. Of 38 AEs, 5 were, at least, possibly related to a CPP transfusion and included DMSO skin odor following a ½ CPP unit and three CPP units (n=2), mild fever and chills in the same patient after one CPP unit (n=2), and moderate headache the next day following transfusion of three CPP units (n=1). As expected in this clinically-ill patient population, D-dimer, fibrinogen, F1+2, aPTT, and TAT averaged higher than the upper limit of normal prior to transfusion and remained similar following transfusion. TGT and TEG were suppressed pre-transfusion and were improved towards normal levels following transfusion of either CPP or standard plts. There was no induction of a post-transfusion hypercoagulable state in any patient based on laboratory results.

Modest increases in corrected plts count increments (x 10³/mm³) were observed following CPP transfusion (one CPP unit gave CCI's of 2.3 ± 3.5; two CPP units 4.2 ± 2.8; and three CPP units 5.6 ± 2.3) compared with 21.1 ± 3.6 after one unit of standard apheresis plts. Notably, all patients had stabilization or improvement of their bleeding following a CPP transfusion including one patient with Grade 4 CNS bleeding who had resolution of neurologic symptoms with no further plt transfusions, and four patients (17%) had WHO bleeding downgraded.

In conclusion, the infusion of up to three sequential units of CPP in patients with severe thrombocytopenia and active bleeding was safe without any evidence of thrombotic complications despite CPP having a procoagulant phenotype resulting from the cryopreservation process. CPP may be efficacious to stop bleeding in thrombocytopenic patients as suggested by stabilization or downgrading of WHO bleeding grades. Phase 2/3 efficacy clinical trials are now indicated.