3. Discussions
Randomized trials, meta-analyses and MAICs indicate that the addition of mAbs to standard treatments such as Rd, VMP, VTd, Kd and Pd has radically changed the scenario for both transplant-eligible and transplant-ineligible patients. Unfortunately, from an extended clinical review of the pivotal randomized phase 3 clinical trials examining the current use of anti-CD38 mAbs in MM, the addition of anti-CD38 mAbs resulted in a higher rate of AEs in the overall population, particularly in terms of infections (including pneumonia) and neutropenia plus lymphocytopenia. In fact, as regards infectious diseases, the FAERS suggests a significant association between daratumumab-based regimens and multiple opportunistic infections [
4] and pivotal randomized phase 3 clinical trials documented that the rates of infectious complications, in particular respiratory tract infections including viral complications, are higher in the anti-CD38 mAbs combination with IMiDs or PIs plus dexamethasone group than IMiDs or PIs and dexamethasone alone. In the same line, a recent metanalysis of clinical trials [
39], pooling five randomized phase 3 studies (ALCYONE, MAIA, CASSIOPEIA, CASTOR and POLLUX), confirmed that the incidence of TD due to infection/pneumonia was slightly higher with daratumumab than in the control group (0.95% vs 0.73%); conversely, the rates of TD due to treatment-emergent adverse events (TEAEs) (6.77% vs 10.08%) and treatment-related deaths (3.61% vs 4.34%) were significantly lower in the daratumumab group than in the control arm. In contrast to anti-CD38 mAbs, the addition of elotuzumab with IMiDs did not result in a higher incidence of treatment-related neutropenia and pneumonia [
36,
37,
38].
Despite these clinical observations, to analyze the severity and outcomes of infectious disease with daratumumab vs comparators, some questions need to be asked. Firstly, it is very interesting to observe that, although grade ≥3 infections (25.7% vs 19.0%) and pneumonia (9.3% s 5.7%) [
5] were reported more frequently in the anti-CD38 mAbs group than in the control group, the incidence of serious AEs and the incidence of infections leading to death were similar compared with control arms [
39]. The safety profile of quadruplet regimens is similar to those of triplet regimens and there is no evidence of additional significant toxicities [
6,
9,
10,
11,
12,
13]. Secondly, van de Donk et al. [
40], using pooled data from patients treated in the ALCYONE and MAIA trials, showed a progressive decrease of the infectious risk after 6 months of treatment (10% vs 20%), and a lower grade ≥3 infection risk in the daratumumab group compared with the standard-of-care arm after 2 years of treatment. In an inter analysis of the ALCYONE trial [
18], after a long median follow-up of 40.1 months, Mateos et al. confirmed that, during maintenance daratumumab monotherapy, the most common AEs observed were respiratory infections of grade 1-2 (up to 19%), suggesting that after more than 3 years of follow-up, the D-VMP group continued to show significant improvements in progression-free survival with no increasing susceptibility to infections. Thirdly, the frailty analyses of ALCYONE [
20] and MAIA [
21] trials, an Italian retrospective clinical study [
41] and a multicenter real-world retrospective experience of patients with RRMM enrolled in compassionate early access programs (EAPs) for Isa-Pd in France [
42] support the clinical benefit of anti-CD38 mAbs-based treatment also in frail patients. In accordance with frailty subanalyses, in the POLLUX trial [
24] no increased toxicity was observed in patients aged ≥75 years; this was probably related to a lower median dose intensity of lenalidomide and dexamethasone than daratumumab with D-Rd vs Rd in all frailty subgroups, suggesting that clinicians were more likely to modify the dose of lenalidomide and/or dexamethasone due to AEs. In fact, the median dose intensity of daratumumab was similar across frailty subgroups (total-non-frail 98.2% vs frail 98.0%). Fourthly, in Isa-Pd arm of the ICARIA trial [
30], the incidence of pneumonia was lower in elderly patients, and this may be due to the higher percentage of older patients receiving prophylactic strategies revealing the efficacy of this approach. In fact, granulocyte-colony stimulating factor was used in 69% of patients in the Isa-Pd group, and 53% in the Pd control arm [
30].
Therefore, based on these data, the increasing susceptibility to infections in patients with anti-CD38 mAbs-treated MM is documented to be multifactorial. In addition to the intrinsic anti-CD38 mAbs effects on the immune system (defects in T-cell function responsible for cytomegalovirus and varicella-zoster reactivation, Pneumocystis Jirovecii Pneumonia; B-cell dysfunction with secondary low immunoglobulin levels causes the emergence of major pathogens including pneumococci, Haemophilus influenza), several other factors are related to the increased infectious risk such as the higher incidence of secondary neutropenia, many prior lines of therapy, the complex schedules and the disease characteristics (disease burden, advanced ISS disease stage, aggressiveness, refractory/relapsed disease). In our recent analysis [
43], in accordance with recent literature data [
44], we emphasized the hypothesis that the disease burden appears to reduce the immunity acquired from vaccinations rather than the treatment type and timing of vaccinations and plays a very important role in the infectious risk.
To prevent infections the three main potential strategies are antimicrobial prophylaxis, vaccinations, and, in patients with significant hypogammaglobulinemia, immunoglobulin substitution therapy. Recommendations for antibiotic prophylaxis are less clear, but a recent randomized study from the UK showed a significant reduction in the rate of infections or death (27% vs 19%) with the addition of prophylactic levofloxacin to active myeloma treatment particularly in transplantation-ineligible patients (HR 0.51) within the first 3 months [
45]. Consensus reports from European experts recommend prophylactic antibiotic treatment in patients at high risk of infectious complications such as elderly patients, those with active, poorly controlled disease, comorbidities, those with a history of an increased incidence of infections and those receiving highly myelotoxic therapy [
46]. Conversely, anti-bacterial prophylaxis may be considered in all other cases. Commonly used antibiotics are co-trimoxazol, amoxicillin/clavulate or levofloxacin. Recent international guidelines recommend fluconazole prophylaxis in cases of a history of fungal infection, prolonged neutropenia or steroid administration [
46]. Recent guidelines also recommend in all patients appropriate vaccinations against pneumococci, influenza, COV-19, Herpes zoster and those bacteria and viruses (haemophilus influenzae, meningococci, and hepatitis) that frequently may pose a significant risk to patients with MM [
46,
47].
Further optimization of myeloma treatment approaches could be, in particular, dexamethasone-free strategies, that can allow patients to remain on treatment longer, maintaining disease control over time and reducing the rates of clinical infections [
48,
49]. Data on a phase 3 trial reported that, in patients receiving Rd, reducing the lenalidomide dose and discontinuing dexamethasone after the first 9 cycles did not affect the efficacy but limited toxicities as compared to full-dose Rd [
48]. Data have been recently reported from the multicenter randomized phase 3 IFM 2017-03 trial evaluating the dexamethasone-sparing regimen of Dara+Lena compared with Lena+Dexa in patients aged ≥65 years with NDMM, classified as frail according to age, comorbidities and ECOG PS ≥2 [
49]. The dexamethasone-sparing regimen of Dara+Lena was associated with higher response rates (ORR 96% vs 85%), and rates of MRD negativity at 10
-5 (10% vs 3%), and a favorable safety profile compared with Lena+Dexa (no increased risk of infection or pneumonia [
p 0.29], and similar TD rates between arms [
p 0.65]) [
49]. The dexamethasone-sparing regimen of Dara+Lena resulted in better tolerability compared with Rd, particularly in terms of non-hematologic toxicities [
49].
In conclusion, some important clinical scenarious should be considered when using anti-CD38 mAbs to treat myeloma patients. Firstly, all data provided by randomized trials, meta-analyses and MAICs have demonstrated that anti-CD38 mAbs-based regimens remain an extraordinary therapeutic approach in NDMM and also in RRMM. The addition of daratumumab enhances the efficacy of standard first-line therapy for transplantation-eligible patients with NDMM and the safety profile of this quadruplet therapy is similar to those of triplet regimens and does not impede proceeding to transplantation. Secondly, the TEAEs did not result in higher treatment interruption rates or fatal AEs, revealing that these hematologic and non-hematologic TEAEs were manageable. Thirdly, based on recent literature data [
18,
40], and according to Dryson et al. [
45], antibacterial prophylaxis might be appropriate and justified during the first months of therapy in particular in frail patients, patients with a high-risk of infections and when the disease burden is high. Fourthly, a dexamethasone-sparing approach can be considered if an infection risk limits treatment tolerability, since there is emerging evidence of similarly effective steroid-sparing regimens [
48,
49].