T-follicular helper cell expansion and chronic T-cell activation are characteristic immune anomalies in Evans syndrome

Biomarkers of Immune Dysregulation and What They Tell Us: Gene Sequencing Is Not the Answer to Every Question

Primary immune regulatory disorders (PIRDs) are inborn errors of immunity, with autoimmune, hyperinflammatory, and lymphoproliferative manifestations as presenting features rather than recurrent infections. Genetic testing remains the primary tool for diagnosing patients with immune defects. Not all suspected PIRDs have a known genetic cause. Many hyperinflammatory disorders require urgent intervention, limiting the usefulness of gene sequencing in some cases. Current clinically approved immunology tests can detect immune dysregulation even without apparent immune deficiency. This review presents commonly known patterns of immune dysregulation that can be detected with currently available immune testing and additional testing in the clinical immunology laboratories' pipeline.

A Room for Long-Lived Plasma Cell Contribution in Immune Cytopenias?

Immune cytopenias, such as autoimmune hemolytic anemia, immune thrombocytopenia, and Evans syndrome, are characterized by autoantibodies targeting various blood cells, initiating their destruction. Interactions between T cells, B cells, their ultimate maturational plasma cell descendants, dendritic cells, and macrophages result in antibody production, including the autoreactive ones. Autoimmune phenomena can be idiopathic or associated with various immune dysregulation conditions or malignancies. Interventions disrupting this complex network at different levels have been used to treat immune cytopenias with certain levels of success. Some cases are known to be refractory to many different therapeutic approaches, including the ones eliminating B cells. In some such cases, targeting plasma cells resulted in disease control. Among plasma cell compartments, unique long-lived plasma cells (LLPCs) residing primarily in the bone marrow, are specialized antibody-producing cells with an extended lifespan, capable of persistently secreting antibodies. LLPCs can evade conventional therapeutic strategies designed to target often-proliferating cells. Research focusing on the role of LLPCs in autoimmune phenomena including immune cytopenias has provided evidence for their role, characterized by the sustained production of autoantibodies. Frequent genetic mutations and progression to other immune dysregulation entities have been reported in a group of children with immune cytopenias. This might provide new insights focusing on the potential underlying genetic and epigenetic mechanisms leading to generation and maintenance of LLPCs in autoimmune disorders. We provide a brief review of LLPC biology and evidence for their role in immune cytopenias with potential future implications in this article.

T cell and autoantibody profiling for primary immune regulatory disorders

Background

Limited clinical tools exist for characterizing primary immune regulatory disorders (PIRD), which are often diagnoses of exclusion. Increased CD4+CXCR5+PD1+ circulating T follicular helper (cTfh) cell percentages have been identified as a marker of active disease in some, but not all, autoimmune disorders.

Objective

To develop a diagnostic approach that combines measurements of cellular and serologic autoimmunity.

Methods

We recruited 71 controls and 101 pediatric patients with PIRD with autoimmunity. Flow cytometry was used to measure CD4+CXCR5+ T cells expressing the chemokine receptors CXCR3 and/or CCR6. IgG and IgA autoantibodies were quantified in 56 patients and 20 controls using a microarray featuring 1616 full-length, conformationally intact protein antigens. The 97.5th percentile in the controls serves as the upper limit of normal for percentages of cTfh cells, CD4+CXCR5+ T cells expressing CXCR3 and/or CCR6, and autoantibody intensity and number.

Results

We found that 27.7% of patients had increased percentages of CD4+CXCR5+PD1+ cTfh cells and 42.5% had increased percentages of CD4+CXCR5+ cells expressing CXCR3 and/or CCR6. Patients had significantly more diverse IgG and IgA autoantibodies than controls and 37.5% had increased numbers of high-titer autoantibodies. Integrating measurements of cTfh cells, CD4+CXCR5+ T cells with CXCR3 and/or CCR6, and numbers of high-titer autoantibodies had 71.4% sensitivity (95% CI: 0.5852 - 0.8158) and 85% specificity (95% CI: 0.6396 - 0.9476) for patients with PIRD compared to controls.

Conclusion

By integrating CD4+ T cell phenotyping and total burden of autoantibodies, this approach provides additional tools for the diagnosis of PIRD lacking clinical diagnostic criteria.

Comprehensive RNA-seq analysis of benign prostatic hyperplasia (BPH) in rats exposed to testosterone and estradiol

The imbalance between estrogen and androgen may be an important mechanism of BPH, but the specific mechanism remains unclear. We used mixed sustained-release pellets made of testosterone and estradiol (T + E2) to stimulate the establishment of a BPH rat model. Compared to the prostate hyperplasia rat model using only androgens, the new prostate hyperplasia rat model can be observed to have better macroscopic and pathological characteristics of prostate hyperplasia. We used RNA-seq and bioinformatics to detect differentially expressed genes (DEGs) between the prostate tissue of the novel benign prostatic hyperplasia rat group and the control group, including 458 DEGs, of which 336 were upregulated and 122 were downregulated. Then, RT-qPCR confirmed the authenticity of sequencing results. The analysis results showed that Kif4a and Mki67 were the top core genes in the PPI network. Moreover, we found that these two genes have a positive correlation with each other in multiple cancer tissues, normal tissues, and cancer cells. The DEGs were mainly involved in mitotic nuclear division, nuclear chromosome segregation, and cytokine cell receptor interactions. DEGs were also regulated by 250 miRNAs. In conclusion, we built a novel T + E2-induced rat BPH model, and discovered potentially important genes, pathways, and miRNA-mRNA regulatory networks.

Red flags to suspect inborn errors of immunity in patients with autoimmune diseases

Inborn errors of immunity are monogenic disorders that predispose patients to immune dysregulation, autoimmunity, and infection. Some autoimmune diseases, such as autoimmune cytopenias, systemic lupus erythematosus, and inflammatory bowel diseases, are increasingly recognized as phenotypes of inborn errors of immunity. The objective of this article was to identify red flags or clinical/laboratory markers to suspect inborn errors of immunity in patients with autoimmune cytopenias, systemic lupus erythematosus, and inflammatory bowel diseases through a systematic literature review. The study followed the systematic reviews and meta-analysis guidelines (PRISMA). After selection, we included 36 articles, and their methodological quality was verified using the Joanna Briggs Institute tools for individual risk of bias analysis. The principal red flags in autoimmune cytopenias are chronic, recurrent, and refractory cytopenias, recurrent infection, severe infectious complications associated with immunosuppressive treatment, and chronic lymphoproliferation. In systemic lupus erythematosus, red flags include age of onset before five years, severe organ involvement, chilblain lesions, and chronic lymphoproliferation. For inflammatory bowel diseases, red flags are an age of onset before two years, resistance to conventional therapies, atypical endoscopic or histologic findings, and consanguineous parents. Autoimmune diseases may be the primary manifestation of inborn errors of immunity in pediatric and adult patients. An early diagnosis of a monogenic disorder allows for the tailoring of effective treatment plans, providing prognostic information to families, and offering genetic counseling.

Role of circulating T follicular helper subsets following Ty21a immunization and oral challenge with wild type S. Typhi in humans

Despite decades of intense research, our understanding of the correlates of protection against Salmonella Typhi (S. Typhi) infection and disease remains incomplete. T follicular helper cells (TFH), an important link between cellular and humoral immunity, play an important role in the development and production of high affinity antibodies. While traditional TFH cells reside in germinal centers, circulating TFH (cTFH) (a memory subset of TFH) are present in blood. We used specimens from a typhoid controlled human infection model whereby participants were immunized with Ty21a live attenuated S. Typhi vaccine and then challenged with virulent S. Typhi. Some participants developed typhoid disease (TD) and some did not (NoTD), which allowed us to assess the association of cTFH subsets in the development and prevention of typhoid disease. Of note, the frequencies of cTFH were higher in NoTD than in TD participants, particularly 7 days after challenge. Furthermore, the frequencies of cTFH2 and cTFH17, but not cTFH1 subsets were higher in NoTD than TD participants. However, we observed that ex-vivo expression of activation and homing markers were higher in TD than in NoTD participants, particularly after challenge. Moreover, cTFH subsets produced higher levels of S. Typhi-specific responses (cytokines/chemokines) in both the immunization and challenge phases. Interestingly, unsupervised analysis revealed unique clusters with distinct signatures for each cTFH subset that may play a role in either the development or prevention of typhoid disease. Importantly, we observed associations between frequencies of defined cTFH subsets and anti-S. Typhi antibodies. Taken together, our results suggest that circulating TFH2 and TFH17 subsets might play an important role in the development or prevention of typhoid disease. The contribution of these clusters was found to be distinct in the immunization and/or challenge phases. These results have important implications for vaccines aimed at inducing long-lived protective T cell and antibody responses.

Frequency of HLA-DR+CD38hi T cells identifies and quantifies T-cell activation in hemophagocytic lymphohistiocytosis, hyperinflammation, and immune regulatory disorders

BACKGROUND

Quantifying T-cell activation is essential for the diagnosis and evaluation of treatment response in various hyperinflammatory and immune regulatory disorders, including hemophagocytic lymphohistiocytosis. Plasma soluble IL-2 receptor (sIL-2R) is a well-established biomarker for evaluating systemic T-cell activation. However, the limited availability of sIL-2R testing could result in delayed diagnosis. Furthermore, high sIL-2R levels may not always reflect T-cell activation.

OBJECTIVES

To address these limitations, this study investigated whether cell surface markers of T-cell activation, HLA-DR, and CD38, as assessed by flow cytometry, could be used to quantify systemic T-cell activation in a variety of inflammatory disease states and examine its correlation with sIL-2R levels.

METHODS

Results for sIL-2R, CXCL9, and ferritin assays were obtained from patient's medical records. Frequency of HLA-DR+CD38high(hi) T-cells was assessed in different T-cell subsets using flow cytometry.

RESULTS

In this study's cohort, activation in total CD8+ T (r = 0.65; P < .0001) and CD4+ (r = 0.42; P < .0001) T-cell subsets significantly correlated with plasma sIL-2R levels. At the disease onset, the frequency of HLA-DR+CD38hi T cells in CD8+ T (r = 0.65, P < .0001) and CD4+ T (r = 0.77; P < .0001) effector memory (TEM) compartments correlated strongly with sIL-2R levels. Evaluation of T-cell activation markers in follow-up samples also revealed a positive correlation for both CD4+ TEM and CD8+ TEM activation with sIL-2R levels; thus, attesting its utility in initial diagnosis and in evaluating treatment response. The frequency of HLA-DR+CD38hi T-cells in the CD8+ TEM compartment also correlated with plasma CXCL9 (r = 0.42; P = .0120) and ferritin levels (r = 0.32; P = .0037).

CONCLUSIONS

This study demonstrates that flow cytometry-based direct T-cell activation assessed by HLA-DR+CD38hi T cells accurately quantifies T-cell activation and strongly correlates with sIL-2R levels across a spectrum of hyperinflammatory and immune dysregulation disorders.

Evaluating the prevalence of inborn errors of immunity in adults with chronic immune thrombocytopenia or Evans syndrome

Inborn errors of immunity (IEIs) are monogenic disorders that predispose patients to immune dysregulation, autoimmunity, and infection. Autoimmune cytopenias, such as immune thrombocytopenia (ITP) and Evans syndrome (a combination of ITP and autoimmune hemolytic anemia), are increasingly recognized phenotypes of IEI. Although recent findings suggest that IEIs may commonly underlie pediatric ITP and Evans syndrome, its prevalence in adult patients with these disorders remains undefined. This study sought to estimate the prevalence of underlying IEIs among adults with persistent or chronic ITP or Evans syndrome using a next-generation sequencing panel encompassing >370 genes implicated in IEIs. Forty-four subjects were enrolled from an outpatient adult hematology clinic at a tertiary referral center in the United States, with a median age of 49 years (range, 20-83). Fourteen subjects (31.8%) had secondary ITP, including 8 (18.2%) with Evans syndrome. No cases of IEI were identified despite a high representation of subjects with a personal history of autoimmunity (45.5%) and early onset of disease (median age at diagnosis of 40 years [range, 2-77]), including 20.5% who were initially diagnosed as children. Eight subjects (18.2%) were found to be carriers of pathogenic IEI variants, which, in their heterozygous state, are not disease-causing. One case of TUBB1-related congenital thrombocytopenia was identified. Although systematic screening for IEI has been proposed for pediatric patients with Evans syndrome, findings from this real-world study suggest that inclusion of genetic testing for IEI in the routine work-up of adults with ITP and Evans syndrome has a low diagnostic yield.

Early B-cell development and B-cell maturation are impaired in patients with active hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is characterized by hyperinflammation and multiorgan dysfunction. Infections, including the reactivation of viruses, contribute to significant disease mortality in HLH. Although T-cell and natural killer cell-driven immune activation and dysregulation are well described, limited data exist on the status of B-cell compartment and humoral immune function in HLH. We noted marked suppression of early B-cell development in patients with active HLH. In vitro B-cell differentiation studies after exposure to HLH-defining cytokines, such as interferon gamma (IFN-γ) and tumor necrosis factor, recapitulated B-cell development arrest. Messenger RNA sequencing of human CD34+ cells exposed to IFN-γ demonstrated changes in genes and pathways affecting B-cell development and maturation. In addition, patients with active HLH exhibited a marked decrease in class-switched memory B (CSMB) cells and a decrease in bone marrow plasmablast/plasma cell compartments. The decrease in CSMB cells was associated with a decrease in circulating T follicular helper (cTfh) cells. Finally, lymph node and spleen evaluation in a patient with HLH revealed absent germinal center formation and hemophagocytosis with associated lymphopenia. Reassuringly, the frequency of CSMB and cTfh improved with the control of T-cell activation. Taken together, in patients with active HLH, these changes in B cells may affect the humoral immune response; however, further immune studies are needed to determine its clinical significance.

Clinical utility of measuring CD4+ T follicular cells in patients with immune dysregulation

Mechanistic studies of autoimmune disorders have identified circulating T follicular helper (cTfh) cells as drivers of autoimmunity. However, the quantification of cTfh cells is not yet used in clinical practice due to the lack of age-stratified normal ranges and the unknown sensitivity and specificity of this test for autoimmunity. We enrolled 238 healthy participants and 130 patients with common and rare disorders of autoimmunity or autoinflammation. Patients with infections, active malignancy, or any history of transplantation were excluded. In 238 healthy controls, median cTfh percentages (range 4.8%-6.2%) were comparable among age groups, sexes, races, and ethnicities, apart from a significantly lower percentages in children less than 1 year of age (median 2.1%, CI: 0.4%-6.8, p < 0.0001). Among 130 patients with over 40 immune regulatory disorders, a cTfh percentage exceeding 12% had 88% sensitivity and 94% specificity for differentiating disorders with adaptive immune cell dysregulation from those with predominantly innate cell defects. This threshold had a sensitivity of 86% and specificity of 100% for active autoimmunity and normalized with effective treatment. cTfh percentages exceeding 12% distinguish autoimmunity from autoinflammation, thereby differentiating two endotypes of immune dysregulation with overlapping symptoms and different therapies.

Evans syndrome caused by a deleterious mutation affecting the adaptor protein SASH3

Increasing evidence suggests multilineage cytopenias (also known as Evans syndrome) may be caused by inborn errors of immunity (IEI) with immune dysregulation. We studied a patient with autoimmune haemolytic anaemia and immune thrombocytopenia and identified a germline mutation in SASH3 (c.862C>T;p.Arg288Ter), indicating a recently identified IEI. Immunohistochemistry performed after clinically indicated splenectomy revealed severe hypoplasia/absence of germinal centres. The autoimmune phenotype was associated with an increased CD21low T-bet+ CD11c+ subset along with decreased regulatory T cells, impaired T-cell proliferation and T-cell exhaustion. The younger brother carries the same SASH3 mutation and shares immunophenotypic features but is currently clinical asymptomatic, indicating heterogeneity of SASH3 deficiency.

The Integration of Patient-Reported Quality of Life and Systemic Biomarkers in Patients with Immune Dysregulation

Background

Patient-reported quality of life measurements are an important method for improving the treatment of patients with a variety of diseases. These tools have been minimally investigated in patients with inborn errors of immunity (IEI). Patients with IEI may have immune dysregulation and autoimmune-mediated multi-system organ involvement, making treatment optimization vitally important. Routine laboratory and radiologic testing are typically used for treatment monitoring; however, these modalities have the potential to miss early organ damage. T follicular helper cells are T cells that contribute to antibody production and are known to be expanded in patients with active autoimmunity. We hypothesized that a combination of patient-reported quality of life measurements, in addition to T follicular helper cell percentages, would help us to better understand the level of disease activity in patients with IEI and autoimmunity.

Methods

Patients with immune dysregulation were consented to provide a blood sample and to complete a questionnaire. The Centers for Disease Control HRQOL-14 tool was utilized for the questionnaire portion, and T follicular helper cell levels were measured from whole blood using surface staining and flow cytometry analysis. Patient disease activity was abstracted from the patient medical record, and this was compared to the questionnaire and whole blood assay results.

Results

A total of 20 patients participated in the study; 8 patients had active disease and the remaining were found to be quiescent. There was no significant difference between the patient-reported general health ratings based on sex, age, disease activity, or category of immune dysregulation (p > 0.05). The cTfh percentages were expanded in patients with active disease as compared to those with quiescent (p < 0.05). However, there was no significant correlation between cTfh percentage and patient-reported unhealthy days from the questionnaire (R2 = 0.113, p > 0.05).

Conclusions

Patients with active immune dysregulation were found to have expanded cTfh percentages as compared to those with quiescent disease, however this was not reflected in patient-reported quality of life questionnaires. Better understanding of disease activity and the patient experience is vital to optimize appropriate treatments and outcomes for patients with IEI and immune dysregulation, and more investigation is needed.

Ibrutinib in combination with rituximab is highly effective in treatment of chronic lymphocytic leukemia patients with steroid refractory and relapsed autoimmune cytopenias

Autoimmune hemolytic anemia (AIHA) and pure red cell aplasia (PRCA) are common complications of CLL. The optimal treatment of steroid refractory AIHA/PRCA is not well established. We conducted a multicenter study of ibrutinib and rituximab in patients with relapsed/refractory to steroids AIHA/PRCA and underlying CLL. Protocol included induction (ibrutinib 420 mg/day and rituximab, 8 weekly and 4 monthly infusions) and maintenance phase with ibrutinib alone until progression or unacceptable toxicity. Fifty patients were recruited (44-warm AIHA, 2-cold AIHA, 4-PRCA). After the induction 34 patients (74%) have achieved complete response, 10 (21.7%) partial response. Median time to hemoglobin normalization was 85 days. With regards to CLL response 9 (19%) patients have achieved CR, 2 (4%) patients-stabilization and 39 (78%)-PR. The median follow-up was 37.56 months. In AIHA group 2 patients had a relapse. Among 4 patients with PRCA 1 patient did not respond, and 1 patient had a relapse after CR, 2 remained in CR. The most common adverse events were neutropenia (62%), infections (72%), gastrointestinal complications (54%). In conclusion ibrutinib in combination with rituximab is an active second-line treatment option for patients with relapsed or refractory AIHA/PRCA and underlying CLL.

Clinical utility of measuring CD4 + T follicular cells in patients with immune dysregulation

Mechanistic studies of autoimmune disorders have identified circulating T follicular helper (cTfh) cells as drivers of autoimmunity. However, the quantification of cTfh cells is not yet used in clinical practice due to the lack of age-stratified normal ranges and the unknown sensitivity and specificity of this test for autoimmunity. We enrolled 238 healthy participants and 130 patients with common and rare disorders of autoimmunity or autoinflammation. Patients with infections, active malignancy, or any history of transplantation were excluded. In 238 healthy controls, median cTfh percentages (range 4.8% - 6.2%) were comparable among age groups, sexes, races, and ethnicities, apart from a significantly lower percentages in children less than 1 year of age (median 2.1%, CI: 0.4% - 6.8, p< 0.0001). Among 130 patients with over 40 immune regulatory disorders, a cTfh percentage exceeding 12% had 88% sensitivity and 94% specificity for differentiating disorders with adaptive immune cell dysregulation from those with predominantly innate cell defects. This threshold had a sensitivity of 86% and specificity of 100% for active autoimmunity and normalized with effective treatment. cTfh percentages exceeding 12% distinguish autoimmunity from autoinflammation, thereby differentiating two endotypes of immune dysregulation with overlapping symptoms and different therapies.

Evans Syndrome as a Possible Complication of Brentuximab Vedotin Therapy for Peripheral T Cell Lymphoma

Recently, Brentuximab Vedotin (BV) has emerged as an important therapy not only for Hodgkin's Lymphoma, but also for CD30-positive T cell lymphomas. Although anemia and thrombocytopenia are common myelosuppressive side effects, to our knowledge, this is the first described case of Evans Syndrome associated with BV therapy. We present the case of a 64-year-old female, diagnosed with relapsed Peripheral T Cell Lymphoma Not Otherwise Specified (PTCL-NOS), who, after receiving six cycles of BV, developed authentic severe autoimmune hemolytic anemia with strong positive direct anti-globulin (Coombs) test, simultaneously associated with severe immune thrombocytopenia. The patient was unresponsive to systemic corticotherapy, but fully recovered after a course of IV immunoglobulin.

mTOR inhibition attenuates cTfh cell dysregulation and chronic T-cell activation in multilineage immune cytopenias

mTOR inhibitors such as sirolimus are increasingly used in the management of multilineage immune cytopenia (m-IC) in children. Although sirolimus is effective in improving IC, it is unclear how sirolimus affects the broader immune dysregulation associated with m-IC. We profiled T- and B-cell subsets longitudinally and measured cytokines and chemokines before and after sirolimus treatment. Eleven of the 12 patients with m-IC who tolerated sirolimus were followed for a median duration of 17 months. All patients had an improvement in IC, and sirolimus therapy did not result in significant decreases in T-, B- and NK-cell numbers. However, the expansion and activation of circulating T follicular helper and the Th1 bias noted before the initiation of sirolimus were significantly decreased. Features of chronic T-cell activation and exhaustion within effector memory compartments of CD4+ and CD8+ T cells decreased with sirolimus therapy. Corresponding to these changes, plasma levels of CXCL9 and CXCL10 also decreased. Interestingly, no significant improvement in the proportion of class-switched memory B cells or frequencies of CD4+ naive T cells were noted. Longer follow-up and additional studies are needed to validate these findings and evaluate the effect of sirolimus on B-cell maturation.

Targeting CD38 in Neoplasms and Non-Cancer Diseases

Simple Summary

CD38 remains an interesting target for anticancer therapy. Its relatively high abundance in neoplasms and crucial impact on NAD+/cADPR metabolism and the activity of T cells allows for changing the immune response in autoimmune diseases, neoplasms, and finally the induction of cell death. Antibody-dependent cell cytotoxicity is responsible for cell death induced by targeting the tumor with anti-CD38 antibodies, such as daratumumab. A wide range of laboratory experiments and clinical trials show an especially promising role of anti-CD38 therapy against multiple myeloma, NK cell lymphomas, and CD19- B-cell malignancies. More studies are required to include more diseases in the therapeutic protocols involving the modulation of CD38 activity.

Abstract

CD38 is a myeloid antigen present both on the cell membrane and in the intracellular compartment of the cell. Its occurrence is often enhanced in cancer cells, thus making it a potential target in anticancer therapy. Daratumumab and isatuximab already received FDA approval, and novel agents such as MOR202, TAK079 and TNB-738 undergo clinical trials. Also, novel therapeutics such as SAR442085 aim to outrank the older antibodies against CD38. Multiple myeloma and immunoglobulin light-chain amyloidosis may be effectively treated with anti-CD38 immunotherapy. Its role in other hematological malignancies is also important concerning both diagnostic process and potential treatment in the future. Aside from the hematological malignancies, CD38 remains a potential target in gastrointestinal, neurological and pulmonary system disorders. Due to the strong interaction of CD38 with TCR and CD16 on T cells, it may also serve as the biomarker in transplant rejection in renal transplant patients. Besides, CD38 finds its role outside oncology in systemic lupus erythematosus and collagen-induced arthritis. CD38 plays an important role in viral infections, including AIDS and COVID-19. Most of the undergoing clinical trials focus on the use of anti-CD38 antibodies in the therapy of multiple myeloma, CD19- B-cell malignancies, and NK cell lymphomas. This review focuses on targeting CD38 in cancer and non-cancerous diseases using antibodies, cell-based therapies and CD38 inhibitors. We also provide a summary of current clinical trials targeting CD38.

Secondary Immune Deficiency and Primary Immune Deficiency Crossovers: Hematological Malignancies and Autoimmune Diseases

Primary immunodeficiencies (PIDs), a heterogenous group of inborn errors of immunity, are predetermined at birth but may evolve with age, leading to a variable clinical and laboratory presentation. In contrast, secondary immunodeficiencies (SIDs) are acquired declines of immune cell counts and or/function. The most common type of SID is a decreased antibody level occurring as a consequence of extrinsic influences, such as an underlying condition or a side effect of some medications used to treat hematological malignancies and autoimmune disorders. Paradoxically, immune deficiencies initially attributed to secondary causes may partly be due to an underlying PID. Therefore, in the era of immune-modulating biologicals, distinguishing between primary and secondary antibody deficiencies is of great importance. It can be difficult to unravel the relationship between PID, SID and hematological malignancy or autoimmunity in the clinical setting. This review explores SID and PID crossovers and discusses challenges to diagnosis and treatment strategies. The case of an immunodeficient patient with follicular lymphoma treated with rituximab illustrates how SID in the setting of hematological cancer can mask an underlying PID, and highlights the importance of screening such patients. The risk of hematological cancer is increased in PID: for example, lymphomas in PID may be driven by infections such as Epstein-Barr virus, and germline mutations associated with PID are enriched among patients with diffuse large B-cell lymphoma. Clues suggesting an increased risk of hematological malignancy in patients with common variable immune deficiency (CVID) are provided, as well as pointers for distinguishing PID versus SID in lymphoma patients. Two cases of patients with autoimmune disorders illustrate how an apparent rituximab-induced antibody deficiency can be connected to an underlying PID. We highlight that PID is increasingly recognized among patients with autoimmune cytopenias, and provide guidance on how to identify PID and distinguish it from SID in such patients. Overall, healthcare professionals encountering patients with malignancy and/or autoimmunity who have post-treatment complications of antibody deficiencies or other immune abnormalities need to be aware of the possibility of PID or SID and how to differentiate them.