To our knowledge this is the first systematic review and meta-analysis to assess RTX effect size on FVC% (MD of 4.57%) and DLCO% (MD of 5.0%) in patients with CTD-ILD, reporting a low but not insignificant level of drug-related adverse effects (13.6% of the pooled cohort). Over 240 pooled patient observations were included for each functional endpoint suggesting RTX may modestly improve or stabilize lung function as an adjunct to traditional immunosuppression.
While the combined effect size on PFT outcomes for CTD-ILD was reported here, it is worth reviewing the individual characteristics and responses to RTX in reported specific diseases. SSc has the highest mortality associated with ILD33 along with the highest ILD prevalence34. Incidentally, studies involving SSc-ILD patients were also the largest represented subtype in our meta-analysis. FVC% appeared to improve after RTX therapy in the combined meta-analysis13, 15, 21, 22, 30 inclusive of the only RCT in our systematic review19. Divergent findings though were reported in 23 patients of a subgroup in the study by Lepri et al 15. Similarly, DLCO in SSc-ILD appeared to stabilize or improve with RTX treatment. The second largest group of represented CTD-ILD in our meta-analysis was ASS-ILD, whose disease-defining manifestations often include inflammatory myopathy, ILD, arthritis, and various hand manifestations 35, 36. ILD prevalence ranges from 67 to 100% based on antibody type and the diagnostic criteria used 37, 38. Our meta-analysis and descriptive review included five studies demonstrating FVC improvement or stability with RTX 17, 20, 26, 27, 31. ILD is also an important comorbidity of RA often associated with similar outcomes to IPF, prompting novel approaches to treatment to improve or extend survival 39. RTX has already been approved for the treatment of joint symptoms while there is less data on the treatment of related ILD. RTX demonstrated stabilization and in some cases, improvement of ILD in patients with RA40. All included studies in our meta-analysis suggested stabilization or improvement of FVC and DLCO 14, 18, 28. ILD associated with primary Sjögren’s syndrome (pSS) occurs less commonly compared to other CTD though contributes to significant morbidity and mortality 41, 42. RTX may be a promising treatment in this setting given the suggested role of B cell hyperactivity in the immunopathogenesis of pSS43. The study by Chen et al in included in this meta-analysis suggests RTX may stabilize pulmonary function in patients with pSS 29.
Data for treatment of the other CTD-ILD with RTX remains limited. ILD prevalence in the idiopathic inflammatory myopathies (IIMs) is about 30–40%, and contributes to an estimated mortality of 40% 44. A recent systematic review suggested immunosuppressive therapies were associated with significant functional improvement for most patients with IIMs and chronic ILD, though the mortality of rapidly progressive disease remains high 45. A case report of four patients on RTX therapy for rapidly progressive lung disease related to anti-MDA5 antibody-positive amyopathic dermatomyositis showed clinically significant improvement in lung function, though post-treatment infection risk was increased 46. ILD is less common in systemic lupus erythematosus (SLE). A large multicenter observational cohort of 147 patients suggested RTX may be a possible maintenance option 47, though little data was provided regarding response of ILD findings to directed treatment. In contrast, there are reports of rituximab-induced interstitial pneumonitis seen in SLE patients 48.
Pooled analysis across a spectrum of CTD-ILD suggested a modest 4–5% increase in both FVC% and DLCO% after treatment with RTX compared to stabilization or slowing of prior decline. Similar effect in improved PFT findings were seen in prior observational and RCTs assessing CYC and MMF in patients with scleroderma-ILD 49–52, as well as azathioprine in one series of CTD patients with fibrotic ILD 53. Specific effect sizes ranged from 1.5–15% in terms of FVC% change. In the majority of included studies for this meta-analysis, patients were considered non-responsive or refractory to typical immunosuppression, suggesting a separate role for the targeting of other immune-mediated or inflammatory processes for RTX. Whether an increase in FVC% or DLCO% of 4 to 5% compared to pre-treatment baseline is clinically relevant (in terms of symptomatic or radiologic improvement), or is sustained with subsequent treatment, was not accounted for in this meta-analysis but remain important caveats to real-world disease management and assessment of risk/benefit ratios, particularly regarding the more prolonged and less immediately reversible immunosuppression associated with RTX. As precedence, one study reported the direct effects of immunosuppressant treatment (not RTX) on patient-reported outcomes and health-related quality of life in scleroderma-ILD patients, noting improvements in PRO scores meeting minimal clinically important differences, but little correlation with baseline or subsequent FVC change 54.
Indeed, cost and concern for serious adverse effects may limit immediate or first-line use of RTX in the treatment of CTD-ILD. Our systematic review suggests RTX was overall well-tolerated and safe in the majority of treated CTD-ILD patients 55, including those on long-term therapy 56. RTX-associated interstitial lung disease (RTX-ILD) or lung injury may be particularly concerning in those with already present lung disease. However, RTX-related lung injury was previously reported more commonly in combination with other chemotherapeutic agents for the treatment of lymphoma, which may confound accurate assessments of causation57. No direct RTX-related ILD or lung injury was reported in our review, highlighted by only a few serious adverse events due to infection with no therapy-related deaths.
There are several limitations to our systematic review and meta-analysis. First, variation in disease subtype and patient characteristics likely increased pooled heterogeneity and limits a true assessment of treatment effect size. We accounted for this with use of a random effects model and estimated the degree of heterogeneity for each endpoint, though still found I2 for example in the quantitative meta-analysis of FVC (I2 = 0%) was low and suggestive of little heterogeneity. It is known though that I2 does not necessarily describe how much an effect size varies but more what proportion of the observed variance would remain if all sampling error could be eliminated. When I2 is near zero dispersion in a forest plot may be minimal but does not suggest the absence of any heterogeneity, particularly when sample sizes in included studies were small with wider standard variations 58. Additional limitations to our meta-analysis include the inability to account for duration of drug exposure, variation in timing of PFT follow-up, and the balance of CTD-ILD subtypes, of which pooled analyses may be weighed by one disease type over another. As presented in Table 1, patients treated with RTX in were also often treated first or concomitantly with other immunosuppressive agents. CYC has previously demonstrated short-term improvement in FVC in SSc-ILD patients, though with a higher incidence of adverse effects 49, 59. AZA as maintenance therapy after six months of CYC did not demonstrate significant FVC improvement in this same disease subtype 60. MMF is thought to be safer and equally effective in the management of CTD-ILD when compared to CYC and AZA49, 53. We could not account for the role of concomitant therapy which may have also contributed to measured effect sizes.