Daratumumab interference in flow cytometric anti-granulocyte antibody testing can be overcome using non-human blocking antibodies

BACKGROUND

Daratumumab (DARA), a human IgG1_K monoclonal antibody targeting CD38, is used to treat refractory multiple myeloma patients. CD38 is expressed on many cell types (RBCs, granulocytes, lymphocytes, etc.), and thus, DARA can interfere with serological tests. Information regarding how DARA affects anti-granulocyte antibody (AGA) testing and optimal neutralization of DARA will help laboratories perform accurate testing.

METHODS

Screening of AGA was performed by the granulocyte agglutination test (GAT) and the flow cytometric granulocyte immunofluorescence test (Flow-GIFT). Samples were tested from patients on DARA (n = 7), non-transfused blood donors (healthy controls, n = 7) and AGA reactive samples (positive controls, n = 5). Two neutralization experiments, CD38 removal with DTT and DARA epitope blockage with mouse anti-CD38, were evaluated.

RESULTS

Positive reactivity of human IgG binding was observed in 5/7 DARA cases when tested by Flow-GIFT; however, all 7 cases had negative GAT agglutination results. Further studies by Flow-GIFT revealed DARA concentrations >0·63 μg/ml bound to granulocytes. DARA binding was negated by DTT though a reduced Flow-GIFT sensitivity was observed in positive control samples due to increased background detection of human IgG. Mouse anti-CD38 neutralized the detection of human IgG observed in DARA-treated patient serum without effecting controls.

CONCLUSION

We established that DARA can interfere with AGA testing, leading to false positive Flow-GIFT results without causing GAT agglutination. DTT treatment increased background binding of secondary antibodies causing a decrease in Flow-GIFT sensitivity. In comparison, blockage of the DARA binding epitope using mouse anti-CD38 antibody was effective in neutralizing DARA interference while maintaining Flow-GIFT sensitivity.

Anti-CD20 monoclonal antibody-dependent phagocytosis of chronic lymphocytic leukaemia cells by autologous macrophages

Unconjugated monoclonal antibodies (mAbs) are an important component of effective combination therapies for chronic lymphocytic leukaemia (CLL). Antibody-dependent phagocytosis (ADP) is a major mediator of mAb cytotoxicity, but there is limited knowledge of the determinants of ADP efficacy. We used macrophages derived in vitro from autologous circulating monocytes to test the effects of mAb structure and concentration, target : effector cell ratio, duration of co-incubation and CLL cell CD20 expression on ADP. Next-generation anti-CD20 mAbs (ofatumumab, ublituximab, obinutuzumab, ocaratuzumab) were significantly more effective at inducing ADP compared to rituximab, but none were as effective as the anti-CD52 mAb alemtuzumab. Ofatumumab (10 μg/ml) used as a representative next-generation anti-CD20 mAb achieved an ADP plateau at 3 h co-incubation with a target : effector ratio of 10 : 1 (mean = 2.1 CLL cells/macrophage, range = 1.5-3.5). At 0.156 μg/ml (the lowest concentration tested) ofatumumab ADP was significantly higher than alemtuzumab. However, ofatumumab-induced ADP did not increase significantly at higher mAb concentrations. We show that anti-CD20 mAb ADP efficacy is determined by the mAb characteristics, target : effector ratio and incubation time. We suggest that preclinical evaluation of anti-CD20 mAbs to understand the determinants of ADP could be useful in designing future combination therapies for CLL.

Chemoimmunotherapy for relapsed/refractory and progressive 17p13-deleted chronic lymphocytic leukemia (CLL) combining pentostatin, alemtuzumab, and low-dose rituximab is effective and tolerable and limits loss of CD20 expression by circulating CLL cells

Chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL) patients with purine analog refractory disease or TP53 dysfunction still have limited treatment options and poor survival. Alemtuzumab-containing chemoimmunotherapy regimens can be effective but frequently cause serious infections. We report a Phase II trial testing the efficacy and tolerability of a short-duration regimen combining pentostatin, alemtuzumab, and low-dose high-frequency rituximab designed to decrease the risk of treatment-associated infections and to limit the loss of CD20 expression by CLL cells. The study enrolled 39 patients with progressive CLL that was either relapsed/refractory (n = 36) or previously untreated with 17p13 deletion (17p13-) (n = 3). Thirteen (33%) patients had both 17p13- and TP53 mutations predicted to be dysfunctional, and eight patients had purine analog refractory CLL without TP53 dysfunction. Twenty-six (67%) patients completed therapy, with only five (13%) patients having treatment-limiting toxicity and no treatment-related deaths. Twenty-two (56%) patients responded to treatment, with 11 (28%) complete responses (four with incomplete bone marrow recovery). Median progression-free survival was 7.2 months, time to next treatment was 9.1 months, and overall survival was 34.1 months. The majority of deaths (82%) were caused by progressive disease, including transformed diffuse large B-cell lymphoma (n = 6). Correlative studies showed that low-dose rituximab activates complement and natural killer cells without a profound and sustained decrease in expression of CD20 by circulating CLL cells. We conclude that pentostatin, alemtuzumab, and low-dose high-frequency rituximab is a tolerable and effective therapy for CLL and that low-dose rituximab therapy can activate innate immune cytotoxic mechanisms without substantially decreasing CD20 expression.

Induced resistance to ofatumumab-mediated cell clearance mechanisms, including complement-dependent cytotoxicity, in chronic lymphocytic leukemia

Ofatumumab (OFA), a human CD20-targeting mAb, kills B lymphocytes using the innate immune system including complement-dependent cytotoxicity (CDC). The efficacy of OFA in patients with chronic lymphocytic leukemia (CLL) is limited by drug resistance, which is not well characterized. To better understand mechanisms of resistance, we prospectively studied CLL cells isolated from blood samples collected before and after in vivo exposure to the initial dose of OFA therapy in 25 patients undergoing their first treatment for progressive CLL. As previously reported, OFA therapy rapidly decreased the absolute lymphocyte count, CD20 expression by CLL cells, and serum complement levels. We now show that after administration of the first dose of OFA, there was a modest rebound in the absolute lymphocyte count and serum complement levels, but substantial ongoing loss of CD20 expression by CLL cells. These post-OFA treatment CLL cells were highly resistant to OFA-mediated CDC but retained sensitivity to alemtuzumab-mediated CDC in vitro. Posttherapy serum OFA levels correlated inversely with both the amount of pretreatment circulating cell-bound CD20 and with the decrease in this value following treatment. In vitro OFA-mediated CDC did not predict clinical responses, and the patients with first-dose reactions to OFA did not have markers of increased complement activation in vivo. We propose that optimal efficacy of CD20- targeted therapy for CLL requires determining an mAb dose size and frequency that optimizes CLL killing without exceeding the capacity of the cytotoxic mechanisms and thus minimizes loss of CD20 expression in the surviving CLL cells.

Complement dependent cytotoxicity in chronic lymphocytic leukemia: ofatumumab enhances alemtuzumab complement dependent cytotoxicity and reveals cells resistant to activated complement

Complement dependent cytotoxicity (CDC) is an important mechanism of action for monoclonal antibodies (mAbs) used in the treatment of chronic lymphocytic leukemia (CLL). We hypothesized that alemtuzumab (ALM) mediated CDC would be increased by the addition of ofatumumab (OFA). CLL cells from 21 previously untreated patients with progressive disease were tested in vitro for mAb binding, complement activation and CDC. The subpopulation of CDC resistant CLL cells was examined for levels of C3b and C5b-9 binding, and expression of complement regulatory proteins. OFA significantly increased complement activation and CDC in ALM-treated CLL cells, suggesting that combining ALM and OFA could improve clinical outcome in patients with CLL. Approximately 10% of CLL cells were resistant to CDC because of lower levels of complement activation or decreased cytotoxicity of activated complement. Improvement of clinical responses will require determining the mechanisms of CDC resistance and developing methods to overcome this problem.

Liver disease and diabetes mellitus

The liver plays an important role in the pathogenesis of NIDDM. More importantly to the clinician is the myriad of situations in which the care of the patient with diabetes is affected by or causes an effect to the liver. Patients with underlying diabetes can present with abnormal liver chemistries, which can represent findings as benign as hepatic steatosis or as severe as cirrhosis of the liver. The medications used to treat diabetes can be potent hepatotoxins. Several primary liver diseases are associated with increased risk of the development of diabetes. Epidemiologically, there seems to be a correlation between diabetes mellitus, the most common endocrinologic disease, and hepatitis C, the leading cause of chronic liver disease in the United States. In the management of end-stage liver disease, both cirrhosis and orthotopic liver transplantation promote glucose intolerance and diabetes in a number of patients through various mechanisms including insulin resistance and impaired insulin secretion. These relationships highlight both the importance of the liver as an endocrine organ and the multisystem aspects of the patient with diabetes mellitus.