Prolidase deficiency, a rare inborn error of immunity, clinical phenotypes, immunological features, and proposed treatments in twins.

BACKGROUND: Prolidase deficiency (PD) is an autosomal recessive inborn multisystemic disease caused by mutations in the PEPD gene encoding the enzyme prolidase D, leading to defects in turnover of proline-containing proteins, such as collagen. PD is categorized as a metabolic disease, but also as an inborn error of immunity. PD presents with a range of findings including dysmorphic features, intellectual disabilities, recurrent infections, intractable skin ulceration, autoimmunity, and splenomegaly. Despite symptoms of immune dysregulation, only very limited immunologic assessments have been reported and standard therapies for PD have not been described. We report twin females with PD, including comprehensive immunologic profiles and treatment modalities used. CASE PRESENTATION: Patient 1 had recurrent infections in childhood. At age 13, she presented with telangiectasia, followed by painful, refractory skin ulcerations on her lower limbs, where skin biopsy excluded vasculitis. She had typical dysmorphic features of PD. Next-generation sequencing revealed pathogenic compound heterozygous mutations (premature stop codons) in the PEPD gene. Patient 2 had the same mutations, typical PD facial features, atopy, and telangiectasias, but no skin ulceration. Both patients had imidodipeptiduria. Lymphocyte subset analysis revealed low-normal frequency of Treg cells and decreased frequency of expression of the checkpoint molecule CTLA-4 in CD4+ TEM cells. Analysis of Th1, Th2, and Th17 profiles revealed increased inflammatory IL-17+ CD8+ TEM cells in both patients and overexpression of the activation marker HLA-DR on CD4+ TEM cells, reflecting a highly activated proinflammatory state. Neither PD patient had specific antibody deficiencies despite low CD4+CXCR5+ Tfh cells and low class-switched memory B cells. Plasma IL-18 levels were exceptionally high. CONCLUSIONS: Immunologic abnormalities including skewed frequencies of activated inflammatory CD4+ and CD8+ TEM cells, decreased CTLA-4 expression, and defects in memory B cells may be a feature of immune dysregulation associated with PD; however, a larger sample size is required to validate these findings. The high IL-18 plasma levels suggest underlying autoinflammatory processes.

Association of a Type 2-Polarized T Cell Phenotype With Methotrexate Nonresponse in Patients With Rheumatoid Arthritis.

OBJECTIVE: Rheumatoid arthritis (RA) is a chronic inflammatory disease mediated through complex immunologic pathways. Among RA patients receiving low-dose methotrexate (MTX) monotherapy, approximately one-half exhibit a meaningful clinical response within the first 6 months of starting treatment. Whether baseline immune phenotypes differ between subsequent MTX responders and nonresponders is unknown. This study utilized comprehensive T cell immunophenotyping to identify specific immunologic pathways associated with MTX-nonresponsive joint inflammation in patients with RA. METHODS: In total, 32 patients with recent-onset RA were treated with MTX therapy. After 6 months, 15 patients were categorized as responders and 17 as nonresponders. Comprehensive blood T cell immunophenotyping, using multiparameter immunofluorescence flow cytometry analyses, was performed at baseline and following 6 months of treatment. RESULTS: Baseline measures of disease activity (Disease Activity Score in 28 joints [DAS28], C-reactive protein level, and erythrocyte sedimentation rate) did not differ between MTX responders and nonresponders following MTX treatment. Frequencies of CD4+ and CD8+ T cells were skewed to favor higher CD4:CD8 T cell ratios in MTX responders compared to nonresponders (P < 0.05). The proportion of inducible costimulator-expressing Treg cells was significantly greater among MTX nonresponders. Interleukin-13 (IL-13)-producing, but not interferon-γ- or IL-17-producing, CD4+ effector memory T (Tem) cells were significantly more frequent in MTX nonresponders (P < 0.05). The ratio of IL-13+:IL-17+ Tem cells among CD4+ Tem cells was 1.9-fold higher in MTX nonresponders compared to responders (P < 0.05). Both the CD4:CD8 T cell ratio and the frequency of IL-13+CD4+ Tem cells correlated with changes in the DAS28 score following MTX treatment, whereas T cell expression of immune checkpoint inhibitor markers (CTLA-4, programmed death 1, and T cell immunoglobulin and mucin domain-containing protein 3) did not differ between MTX responders and nonresponders. CONCLUSION: We observed a bias toward type 2-polarized T cell inflammatory responses in the peripheral blood of MTX-nonresponsive RA patients. Targeting the IL-13+CD4+ T cell pathway could be a new therapeutic strategy in RA patients whose disease remains resistant to MTX.

Reconstitution models to evaluate natural killer T cell function in tumor control.

Natural killer T (NKT) cells are glycolipid-reactive T lymphocytes that function in immunosurveillance and immune regulation. However, reduced tumor control in NKT cell-deficient Jα18(-/-) mice may be confounded by an overall reduction in T-cell receptor (TCR) repertoire diversity in these animals. Mechanistic studies are also hindered by a lack of tools to target molecules specifically in NKT cells. To address these issues, we developed protocols to expand functional NKT cells and stably reconstitute them in Jα18(-/-) mice. In vivo delivery of α-galactosylceramide (α-GalCer)-loaded dendritic cells expanded NKT cells in wild-type mice without skewing CD4 or TCR Vß expression profiles. Expanded NKT cells exhibited enhanced cytokine responses upon re-stimulation with glycolipid or CD3 ligation. Adoptive transfer of recently expanded wild-type or interferon (IFN)-γ(-/-) NKT cells protected recipient Jα18(-/-) mice from B16 melanoma metastasis without the need for additional glycolipid stimulation. However, NKT cell reconstitution in recipient Jα18(-/-) mice was short lived. Long-term reconstitution was only achieved when expanded NKT cells were transferred into sublethally irradiated recipients. Thirty days after transfer, NKT cell numbers, phenotype and α-GalCer-induced cytokine responses were equivalent to naive wild-type mice. Jα18(-/-) recipients reconstituted with wild-type or IFN-γ(-/-) NKT cells were both protected from B16 melanoma metastasis following α-GalCer treatment, and NK cell transactivation was intact in mice reconstituted with IFN-γ(-/-) NKT cells. These studies validate the use of reconstitution protocols to investigate the mechanisms of NKT cell immune function, demonstrating that NKT cell-derived IFN-γ and the altered TCR repertoire in Jα18(-/-) mice do not impact NKT cell-mediated antitumor responses.

Regulation of NKT Cell Localization in Homeostasis and Infection.

Natural killer T (NKT) cells are a specialized subset of T lymphocytes that regulate immune responses in the context of autoimmunity, cancer, and microbial infection. Lipid antigens derived from bacteria, parasites, and fungi can be presented by CD1d molecules and recognized by the canonical T cell receptors on NKT cells. Alternatively, NKT cells can be activated through recognition of self-lipids and/or pro-inflammatory cytokines generated during infection. Unlike conventional T cells, only a small subset of NKT cells traffic through the lymph nodes under homeostatic conditions, with the largest NKT cell populations localizing to the liver, lungs, spleen, and bone marrow. This is thought to be mediated by differences in chemokine receptor expression profiles. However, the impact of infection on the tissue localization and function of NKT remains largely unstudied. This review focuses on the mechanisms mediating the establishment of peripheral NKT cell populations during homeostasis and how tissue localization of NKT cells is affected during infection.

Natural killer T cell activation overcomes immunosuppression to enhance clearance of postsurgical breast cancer metastasis in mice.

Metastatic lesions are responsible for over 90% of breast cancer associated deaths. Therefore, strategies that target metastasis are of particular interest. This study examined the efficacy of natural killer T (NKT) cell activation as a post-surgical immunotherapy in a mouse model of metastatic breast cancer. Following surgical resection of orthotopic 4T1 mammary carcinoma tumors, BALB/c mice were treated with NKT cell activating glycolipid antigens (α-GalCer, α-C-GalCer or OCH) or α-GalCer-loaded dendritic cells (DCs). Low doses of glycolipids transiently reduced metastasis but did not increase survival. A high dose of α-GalCer enhanced overall survival, but was associated with increased toxicity and mortality at early time points. Treatment with α-GalCer-loaded DCs limited tumor metastasis, prolonged survival, and provided curative outcomes in ∼45% of mice. However, survival was not increased further by additional DC treatments or co-transfer of expanded NKT cells. NKT cell activation via glycolipid-loaded DCs decreased the frequency and immunosuppressive activity of myeloid derived suppressor cells (MDSCs) in tumor-resected mice. In vitro, NKT cells were resistant to the immunosuppressive effects of MDSCs and were able to reverse the inhibitory effects of MDSCs on T cell proliferation. NKT cell activation enhanced antitumor immunity in tumor-resected mice, increasing 4T1-specific cytotoxic responses and IFNγ production from natural killer (NK) cells and CD8+ T cells. Consistent with increased tumor immunity, mice surviving to day 150 were resistant to a second tumor challenge. This work provides a clear rationale for manipulating NKT cells to target metastatic disease.

Regulation of cytokine polarization and T cell recruitment to inflamed paws in mouse collagen-induced arthritis by the chemokine receptor CXCR6.

OBJECTIVE: The chemokine receptor CXCR6 is highly expressed on lymphocytes isolated from the synovium of patients with rheumatoid arthritis, psoriatic arthritis, or juvenile idiopathic arthritis, suggesting that CXCR6 regulates immune cell activation or infiltration into arthritic joints. This study was undertaken to examine the role of CXCR6 in T cell activation and arthritis development. METHODS: A collagen-induced arthritis model was used to examine arthritis development in wild-type and CXCR6(-/-) mice. CXCR6 expression, lymphocyte accumulation, and intracellular cytokine production were examined by flow cytometry. Collagen-specific antibodies were measured in the serum. Collagen-specific recall responses were examined in vitro via proliferation and cytokine release assays. T cell homing to inflamed joints was examined using competitive adoptive transfer of dye-labeled lymphocytes from wild-type and CXCR6(-/-) mice. RESULTS: The numbers of CXCR6+ T cells were increased in the paws and draining lymph nodes of arthritic mice. The incidence of arthritis, disease severity, extent of T cell accumulation, and levels of collagen-specific IgG2a antibodies were significantly reduced in CXCR6(-/-) mice compared to wild-type mice. T cells from wild-type mice exhibited Th1 (interferon-γ [IFNγ]) polarization in the inguinal lymph nodes following immunization. At disease peak, this shifted to a Th17 (interleukin-17A [IL-17A]) response in the popliteal lymph nodes. T cells in CXCR6(-/-) mice exhibited impaired cytokine polarization, resulting in a decreased frequency and number of IL-17A- and IFNγ-producing cells. Recruitment of activated CXCR6(-/-) mouse T cells to the inflamed paws was impaired compared to recruitment of wild-type mouse T cells. CONCLUSION: These experiments demonstrate that CXCR6 plays important roles in the pathogenesis of arthritis through its effects on both T cell cytokine polarization and homing of T cells to inflamed joints.

CCR4 and CXCR3 play different roles in the migration of T cells to inflammation in skin, arthritic joints, and lymph nodes.

CCR4 and CXCR3 are expressed on several T-cell subsets in inflamed tissues, yet their role in tissue-specific recruitment is unclear. We examined the contributions of CCR4 and CXCR3 to T-cell recruitment into inflamed joints in collagen-induced arthritis, antigen-draining lymph nodes (LNs) and dermal inflammatory sites (poly I:C, LPS, concanavalin A, and delayed type hypersensitivity), using labeled activated T cells from CXCR3(-/-), CCR4(-/-), and WT mice. Both CXCR3 and CCR4 deficiency reduced the development of arthritis, but did not affect Th1-cell recruitment to the inflamed joints. Accumulation in inflamed LNs was highly CXCR3 dependent. In contrast, CCR4-deficient Th1 cells had an increased accumulation in these LNs. Migration to all four dermal inflammatory sites by activated Th1 and T cytotoxic cells and memory CD4(+) T cells was partially CXCR3-dependent, but Treg-cell migration was independent of CXCR3. The subset of cells expressing CCR4 has skin-migrating properties, but CCR4 itself is not required for the migration. Thus, migration into these inflamed tissues is CCR4-independent, and partially dependent on CXCR3, except for Treg cells, which require neither receptor. CCR4 may therefore affect retention of T cells in different tissues rather than trafficking out of the blood.