Concepts in immuno-oncology: tackling B cell malignancies with CD19-directed bispecific T cell engager therapies.

The B cell surface antigen CD19 is a target for treating B cell malignancies, such as B cell precursor acute lymphoblastic leukemia and B cell non-Hodgkin lymphoma. The BiTE® immuno-oncology platform includes blinatumomab, which is approved for relapsed/refractory B cell precursor acute lymphoblastic leukemia and B cell precursor acute lymphoblastic leukemia with minimal residual disease. Blinatumomab is also being evaluated in combination with other agents (tyrosine kinase inhibitors, checkpoint inhibitors, and chemotherapy) in various treatment settings, including frontline protocols. An extended half-life BiTE molecule is also under investigation. Patients receiving blinatumomab may experience cytokine release syndrome and neurotoxicity; however, these events may be less frequent and severe than in patients receiving other CD19-targeted immunotherapies, such as chimeric antigen receptor T cell therapy. We review BiTE technology for treating malignancies that express CD19, analyzing the benefits and limitations of this bispecific T cell engager platform from clinical experience with blinatumomab.

The assessment of immune-regulatory effects of extracorporeal photopheresis in systemic sclerosis: a long-term follow-up study.

The therapeutic options in systemic sclerosis (SSc) are limited mainly to the management of complications, and decelerating fibrosis and preventing disease progression are still great challenges. Extracorporeal photopheresis (ECP) is one of the promising therapeutic strategies in SSc; nevertheless, there is no consensus on the ideal timing and frequency of treatment cycles. In the present study, we evaluated the long-term effects of consecutive ECP treatments, and the stability of clinical and laboratory improvements. We enrolled nine patients with diffuse cutaneous SSc and performed 12 ECP cycles (24 ECP treatments) per patient in total. ECP cycles were carried out once in every 6 weeks, and each cycle consisted of two procedures. Sixteen healthy individuals served as controls for laboratory assessment. Following the sixth ECP cycle, we observed further improvement in skin score, which was confirmed by high-resolution ultrasonography as well. After the second ECP cycle, values of Tr1 and CD4+CD25(bright) Treg cells increased; however, Tr1 cells remained under control values until the 10th cycle. Suppressor activity of CD4+CD25+ Treg cells improved, while percentages of Th17 cells decreased. At the end of 12-month follow-up, we did not observe significant deterioration in skin involvement; however, improvement in laboratory parameters diminished after 12 months. If the first six ECP cycles are effective, uninterrupted continuation of treatment should be considered, which may lead to the normalization of Tr1 cell values along with further clinical improvement. Our laboratory observations indicate that immunomodulatory effect of ECP treatments lasts for 1 year only.

Simultaneous assessment of rotavirus-specific memory B cells and serological memory after B cell depletion therapy with rituximab.

The mechanisms that contribute to the maintenance of serological memory are still unclear. Rotavirus (RV) memory B cells (mBc) are enriched in IgM(+) and CD27- subpopulations, which are associated with autoimmune diseases pathogenesis. In patients with autoimmune diseases treated with Rituximab (RTX), some autoantibodies (auto-Abs) decrease after treatment, but other auto-Abs and pathogen-specific IgG Abs remain unchanged. Thus, maintenance of autoimmune and pathogen-specific serological memory may depend on the type of antigen and/or Ab isotype evaluated. Antigen-specific mBc and antigen-specific Abs of different isotypes have not been simultaneously assessed in patients after RTX treatment. To study the relationship between mBc subpopulations and serological memory we characterized total, RV- and tetanus toxoid (TT)-specific mBc by flow cytometry in patients with autoimmune diseases before and after treatment with RTX. We also measured total, RV- and TT-Abs, and some auto-Abs by kinetic nephelometry, ELISA, and EliA tests, respectively. Minor differences were observed between the relative frequencies of RV-mBc in healthy controls and patients with autoimmune disease. After RTX treatment, naïve Bc and total, RV- and TT-specific mBc [IgM(+), switched (IgA(+)/IgG(+)), IgM(+) only, IgD(+) only, and CD27- (IgA(+)/IgG(+)/IgM(+))] were significantly diminished. An important decrease in total plasma IgM and minor decreases in total IgG and IgA levels were also observed. IgM rheumatoid factor, IgG anti-CCP, and IgG anti-dsDNA were significantly diminished. In contrast, RV-IgA, RV-IgG and RV-IgG1, and TT-IgG titers remained stable. In conclusion, in patients with autoimmunity, serological memory against RV and TT seem to be maintained by long-lived plasma cells, unaffected by RTX, and an important proportion of total IgM and serological memory against some auto-antigens seem to be maintained by short-lived plasma cells, dependent on mBc precursors depleted by RTX.

Lymphocyte subsets in healthy Malawians: implications for immunologic assessment of HIV infection in Africa.

BACKGROUND: CD4(+)T lymphocyte measurements are the most important indicator of mortality in HIV-infected individuals in resource-limited settings. There is currently a lack of comprehensive immunophenotyping data from African populations to guide the immunologic assessment of HIV infection. OBJECTIVE: To quantify variation in absolute and relative lymphocyte subsets with age in healthy Malawians. METHODS: Lymphocyte subsets in peripheral blood of 539 healthy HIV-uninfected Malawians stratified by age were enumerated by flow cytometry. RESULTS: B and T-lymphocyte and T-lymphocyte subset absolute concentrations peaked in early childhood then decreased to adult levels, whereas lymphocyte subset proportions demonstrated much less variation with age. Adult lymphocyte subsets were similar to those in developed countries. In contrast, high B-lymphocyte and CD8(+)T-lymphocyte levels among children under 2 years, relative to those in developed countries, resulted in low CD4(+)T-lymphocyte percentages that varied little between 0 and 5 years (35% to 39%). The CD4(+)T-lymphocyte percentages in 35% of healthy children under 1 year and 18% of children age 1 to 3 years were below the World Health Organization threshold defining immunodeficiency in HIV-infected children in resource-limited settings. Thirteen percent of healthy children under 18 months old had a CD4:CD8T-lymphocyte ratio <1.0, which is commonly associated with HIV infection. All immunologic parameters except absolute natural killer lymphocyte concentration varied significantly with age, and percentage and overall absolute CD4(+)T-lymphocyte counts were higher in females than males. CONCLUSION: Although lymphocyte subsets in Malawian adults are similar to those from developed countries, CD4(+)T-lymphocyte percentages in young children are comparatively low. These findings need to be considered when assessing the severity of HIV-related immunodeficiency in African children under 3 years.

Estimating hypermutation rates from clonal tree data.

To understand the mechanisms underlying the varying patterns of mutations that occur during immune and autoimmune responses, estimates of the somatic hypermutation rate are critical. However, despite its significance, precise estimates of the mutation rate do not currently exist. Microdissection studies of mutating B cell clones provide an opportunity to measure this rate more accurately than previously possible. Each microdissection provides a number of clonally related sequences that, through the analysis of shared mutations, can be genealogically related to each other. The shape of these clonal trees is influenced by many processes, including the hypermutation rate. We have developed two different methods to estimate the mutation rate based on these data. These methods are applied to two sets of experimental data, one from an autoimmune response and one from the antihapten response to (4-hydroxy-3-nitrophenyl)acetyl (NP). Comparable mutation rates are estimated for both responses, 0.7-0.9 x 10(-3) and 0.9-1.1 x 10(-3) bp(-1) division(-1) for the autoimmune and NP responses, respectively. In addition to comparing the results of the two procedures, we investigate the effect on our estimate of assumptions, such as the fraction of lethal mutations.

Models for antigen receptor gene rearrangement. III. Heavy and light chain allelic exclusion.

The extent of allelic exclusion in Ig genes is very high, although not absolute. Thus far, it has not been clearly established whether rapid selection of the developing B cell as soon as it has achieved the first productively rearranged, functional heavy chain is the only mechanism responsible for allelic exclusion. Our computational models of Ag receptor gene rearrangement in B lymphocytes are hereby extended to calculate the expected fractions of heavy chain allelically included newly generated B cells as a function of the probability of heavy chain pairing with the surrogate light chain, and the probability that the cell would test this pairing immediately after the first rearrangement. The expected fractions for most values of these probabilities significantly exceed the levels of allelic inclusion in peripheral B cells, implying that in most cases productive rearrangement and subsequent cell surface expression of one allele of the heavy chain gene probably leads to prevention of rearrangement completion on the other allele, and that additional mechanisms, such as peripheral selection disfavoring cells with two productively rearranged heavy chain genes, may also play a role. Furthermore, we revisit light chain allelic exclusion by utilizing the first (to our knowledge) computational model which addresses and enumerates B cells maturing with two productively rearranged kappa light chain genes. We show that, assuming that there are no selection mechanisms responsible for abolishing cells expressing two light chains, the repertoire of newly generated B lymphocytes exiting the bone marrow must contain a significant fraction of such kappa double-productive B cells.

Immunophenotypic and functional characterization of human umbilical cord blood mononuclear cells.

Human umbilical cord blood (CB) represents a unique source of transplantable hematopoietic progenitor cells. Potential advantages of using CB relate to the high number and quality of hematopoietic stem and progenitor cells present in the circulation at birth and to the relative immune immaturity of the newborn immune cells. Discussed in this review are: (a) Quantity and quality of immature hematopoietic stem and progenitor cells from cord blood; (b) Immune cells in cord blood including the number of B- and T-lymphocytes, as well as natural killer cells and characterization of their functional capacities; (c) The need of an international CB transplantation registry and the availability of cord blood banks. Although still in its infancy, human CB progenitor cells hold considerable potential for in vitro expansion and to transplant the adult recipients. In addition, the CB repopulating progenitor cells can serve as targets for gene transfer and long-term treatment of genetic inherited diseases, cancer and some immunodeficiencies.