Short Daratumumab Consolidation in Patients with AL Amyloidosis or Lcdd Improves Complete Response Rates and Modifies Bone Marrow Microenvironment

A deep and profound hematologic response is associated with substantial improvement in the probability of improvement in organ function and survival in patients with AL amyloidosis or LCDD. Bortezomib-based therapy is the mainstay of anti-clonal therapy for AL amyloidosis and LCDD, however, hemCR is achieved in only 20% of patients. Daratumumab has shown to be active and able to induce rapid responses in patients with AL amyloidosis. Plasma cell clones in AL are small and indolent and further improvement of hematologic response could be achieved by consolidation strategies. Given the activity of daratumumab and the rapid induction of deep responses in AL amyloidosis, we treated patients with AL amyloidosis or LCDD , who had not achieved a hemCR after standard therapy, with a short course of daratumumab. In consenting patients, we evaluated MRD in the bone marrow (BM), before and after consolidation, by means of next generation multiparametric flow cytometry (NGF-MFC), using the Euroflow protocol. Thus, beyond the presence of MRD , we were able to evaluate also other components of the BM microenvironment and their changes before and after daratumumab.

All patients were treated in the Department of Clinical Therapeutics, Athens, Greece. The study included patients who had achieved either PR or VGPR after completing standard bortezomib-based primary therapy. Consolidation included 4 weekly infusions of daratumumab 16 mg/kg. Pre-emptive therapy for IRR was given starting two days before the first infusion of daratumumab that included low dose steroids (equivalent of 16 mg of methylprednisolone), H1 & H2 inhibitors and montelukast.

Twenty-five patients (20 with AL and 5 with LCDD) received daratumumab consolidation. Among patients with AL amyloidosis, median age is 65, kidneys and heart were involved in 70% and 75% respectively, baseline Mayo stage was 20%, 70% and 10% for stage 1,2 & 3 respectively. Baseline immunofixation in serum or urine was positive in all patients, median baseline dFLC at diagnosis was 125 mg/L (range 60-7228). Median time from start of first line therapy to daratumumab consolidation was 7 months and all patients had completed their planned therapy. At the time of initiation of daratumumab, 24 patients were in VGPR and one in PR and the median dFLC level was 12 mg/L; all had positive serum or urine immunofixation and in all patients MRD was detectable by NGF-MFC. Except for one patient, all the others received the planned 4 daratumumab infusion. Mild IRRs occurred in 3 patients (grade 1 in 2 and grade 2 in one patient); no IRRs occurred after the first infusion.

One month after completion of consolidation with daratumumab, median dFLC dropped to 5 mg/L and 10 (40%) of the patients improved their response: 36% from VGPR to hemCR and one patient with PR to VGPR. Among those that achieved a hemCR, 5 (50%) became MRD negative by NGF-MFC. However, even among those that remained MRD-positive there was a decrease in the number of aberrant plasma cells (APCs) by a median of one log. In MRD-positive patients a change in the composition of the remaining phenotypic subclones of APCs was also observed. Regarding the other BM cell populations, we observed statistically significant changes in B-cell precursors (increased from 14.32%+/-11.75% to 34.76% +/-24.11%, p=0.0004), naïve B-cells (decreased from 65.58%+/-17.56% to 47.37%+/-22.66%, p=0.0003), T cells (increased from 6.44% +/- 2.78% to 10.86%+/- 6.407%, p=0.0007), CD27+ NK & NKT cells (increased from 15.65% +/-13.5% to 36.34%+/- 24.43%, p=0.0002), mast cells (increased from 0.0092%+/-0.0123% to 0.011%+/-0.012%, p=0.002) and erythroblasts (increased from 1.82%+/-0.97% to 2.41%+/- 1.03%, p=0.076). Due to the small numbers it was not possible to make meaningful comparison between MRD positive and negative patients. However, the above results indicate that even a short course of daratumumab was able to cause significant changes in the BM microenvironment of these patients. From this small prospective study we conclude that consolidation with a short course of daratumumab can improve the depth of response in patients with AL or LCDD that have not achieved a hemCR after primary therapy, even to the depth of undetected MRD. In addition, daratumumab causes significant changes in the BM environment, which need further investigation in order to understand their implications.