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Objective. Despite its widespread and increasingly diverse usage, the long-term immunologic effects of B cell depletion with rituximab are not well defined. Critical gaps in our knowledge include the phenotype of reconstituting B cells, the kinetics of regeneration of mature naïve and memory B cells, and the impact of B cell depletion on specific immune functions and ultimately the re-establishment of immunological tolerance.
Methods. As part of a phase I/II dose-escalation trial of rituximab in SLE (n=10) and two clinical trials of rituximab combined with either a CpG oligonucleotide or an anti-idiotype vaccine in the treatment of follicular NHL (n=11), we comprehensively evaluated the phenotype and kinetics of returning B cells after rituximab therapy. Transitional B cells were further phenotyped based on multiple surface markers and functional parameters (proliferation, immunoglobulin secretion, induction of apoptosis, and ability to extrude rhodamine123).
Results. During the B cell reconstitution phase in the majority of patients a high fraction of the peripheral blood B cells have a transitional phenotype, similar to what has been described during the original ontogeny of the immune system and following bone marrow transplantation (SLE: 24.7% + 13.7%, compared to baseline for this cohort of 3.5% + 2.7%, p=0.0008; compared to controls of 4.4% + 2.4%, p=0.00002) (lymphoma: range 17-84%). Strikingly, SLE patients who experienced prolonged clinical remission were characterized by the persistence of elevated numbers of transitional B cells and a scarcity of CD27+ memory B cells for several years after treatment. Of additional note, the patients attaining prolonged remission lacked baseline antibodies against ribonucleoprotein antigens (p=0.002). We find that the newly formed B cells are more heterogeneous than previously described, with decreasing CD24 and CD38 expression during maturation from presumed T1 to T2 stages and variable CD10 expression. Moreover, a subset of B cells that appear to be naïve based on CD24, CD38, and IgD expression behave functionally like transitional cells with failure to extrude rhodamine123, reduced proliferation, and increased apoptosis, suggesting developmental stages in between T2 and naïve.
Conclusions. These results suggest fundamental differences in the B cell depletion and/or reconstitution process experienced by different groups of patients that impact clinical and immunologic outcomes. Additionally, the expansion of functionally immature B cells and delay in memory B cell recovery suggests the need for careful monitoring of humoral responses and for a better understanding of infectious risks and response to vaccination in rituximab treated patients.
Methods. As part of a phase I/II dose-escalation trial of rituximab in SLE (n=10) and two clinical trials of rituximab combined with either a CpG oligonucleotide or an anti-idiotype vaccine in the treatment of follicular NHL (n=11), we comprehensively evaluated the phenotype and kinetics of returning B cells after rituximab therapy. Transitional B cells were further phenotyped based on multiple surface markers and functional parameters (proliferation, immunoglobulin secretion, induction of apoptosis, and ability to extrude rhodamine123).
Results. During the B cell reconstitution phase in the majority of patients a high fraction of the peripheral blood B cells have a transitional phenotype, similar to what has been described during the original ontogeny of the immune system and following bone marrow transplantation (SLE: 24.7% + 13.7%, compared to baseline for this cohort of 3.5% + 2.7%, p=0.0008; compared to controls of 4.4% + 2.4%, p=0.00002) (lymphoma: range 17-84%). Strikingly, SLE patients who experienced prolonged clinical remission were characterized by the persistence of elevated numbers of transitional B cells and a scarcity of CD27+ memory B cells for several years after treatment. Of additional note, the patients attaining prolonged remission lacked baseline antibodies against ribonucleoprotein antigens (p=0.002). We find that the newly formed B cells are more heterogeneous than previously described, with decreasing CD24 and CD38 expression during maturation from presumed T1 to T2 stages and variable CD10 expression. Moreover, a subset of B cells that appear to be naïve based on CD24, CD38, and IgD expression behave functionally like transitional cells with failure to extrude rhodamine123, reduced proliferation, and increased apoptosis, suggesting developmental stages in between T2 and naïve.
Conclusions. These results suggest fundamental differences in the B cell depletion and/or reconstitution process experienced by different groups of patients that impact clinical and immunologic outcomes. Additionally, the expansion of functionally immature B cells and delay in memory B cell recovery suggests the need for careful monitoring of humoral responses and for a better understanding of infectious risks and response to vaccination in rituximab treated patients.
J.H. Anolik, Genentech, 2 Research grants; Genentech, 5 Consulting fees.