Rosiglitazone and trametinib exhibit potent anti-tumor activity in a mouse model of muscle invasive bladder cancer.

Muscle invasive bladder cancers (BCs) can be divided into 2 major subgroups-basal/squamous (BASQ) tumors and luminal tumors. Since Pparg has low or undetectable expression in BASQ tumors, we tested the effects of rosiglitazone, Pparg agonist, in a mouse model of BASQ BC. We find that rosiglitazone reduces proliferation while treatment with rosiglitazone plus trametinib, a MEK inhibitor, induces apoptosis and reduces tumor volume by 91% after 1 month. Rosiglitazone and trametinib also induce a shift from BASQ to luminal differentiation in tumors, which our analysis suggests is mediated by retinoid signaling, a pathway known to drive the luminal differentiation program. Our data suggest that rosiglitazone, trametinib, and retinoids, which are all FDA approved, may be clinically active in BASQ tumors in patients.

Adverse Pregnancy and Child Outcomes in Oral Retinoid-Exposed Pregnancies: A Nationwide Population-Based Study.

BACKGROUND: Oral retinoids are used to treat various dermatological conditions, and their use is increasing in women of childbearing age. However, there is limited knowledge on the incidence of adverse outcomes after retinoid exposure during pregnancy. We aimed to evaluate the risk of adverse outcomes associated with oral retinoid exposure during pregnancy. METHODS: We conducted a retrospective cohort study using the NHIS mother-child linked healthcare database in South Korea. We included all women who gave live birth from April 1, 2009 to December 31, 2020 and their children. The exposure was defined as having ≥ 1 prescription of isotretinoin, alitretinoin, and acitretin from one month before pregnancy to the delivery. The outcomes of interest were adverse child outcomes including major congenital malformations, low birth weight, and neurodevelopmental disorders (autism spectrum disorder and intellectual disorder), and adverse pregnancy outcomes including gestational diabetes mellitus, preeclampsia, and postpartum hemorrhage. Propensity score-based matching weights were used to control for various potential confounders. For congenital malformation, low birth weight, and adverse pregnancy outcomes, we calculated relative risk (RR) with 95% confidence interval (CI) using a generalized linear model and for neurodevelopmental disorders, we estimated hazard ratio (HR) with 95% CI using the Cox proportional hazard model. RESULTS: Of 3,894,184 pregnancies, we identified 720 pregnancies (0.02%) as the oral retinoid-exposed group. The incidence of major congenital malformation was 400.6 per 10,000 births for oral retinoid-exposed group and 357.9 per 10,000 births for unexposed group and the weighted RR was 1.10 (95% CI, 0.65-1.85) in oral retinoid-exposed group compared with unexposed group. The neurodevelopmental disorder showed a potential increased risk, with the weighted HR of 1.63 (95% CI, 0.60-4.41) for autism spectrum disorder and 1.71 (95% CI, 0.60-4.93) for the intellectual disorder, although it did not reach statistical significance. For low birth weight and adverse pregnancy outcomes, no association was observed with oral retinoid exposure during pregnancy. CONCLUSION: This study found no significantly increased risk of congenital malformations, autism spectrum disorders, and intellectual disability associated with oral retinoid exposure during pregnancy; however, given the limitations such as including only the live births and increased point estimate, potential risk cannot be fully excluded.

Acquired epidermodysplasia verruciformis syndrome in HIV-infected patients: a systematic review.

Congenital epidermodysplasia verruciformis (CEV) is a Genodermatosis linked to different inheritance patterns and mutations of the EVER1/TMC6 and EVER2/TMC8 genes. There is an acquired form (AEV) associated with immunodeficiency states, including human immunodeficiency virus (HIV) infection; however, the literature about AEV is limited and imprecise, so a systematic review was performed. A search of the main databases from 1975 to 2021 identified 126 studies, of which 80 met the inclusion criteria. The diagnosis of AEV is complex due to atypical manifestations and locations, it requires a mean follow-up of 7 years, and the lesions do not change with ART therapy, CD4 count, or viral load. Histopathological findings are variable depending on the location of the lesions. HPV 5 remains the serotype most frequently associated with AEV and CEV, although HPV 20 is more frequent than HPV 8 in AEV. Most treatments have low efficacy, the most described are glycolic acid 15%, 5-fluorouracil 5%, imiquimod 5%, and topical retinoids all of them in monotherapy or combined with cryotherapy. Other alternatives include topical cidofovir and systemic retinoids with variable results. The oncologic prognosis is still inconclusive; however, the development of squamous cell carcinoma and melanoma are frankly lower concerning CEV. This review opens new opportunities for future research. Additionally, we provide clear and useful key points for the practice of dermatologists and all professionals treating HIV patients around the world.

An Overview on the Management of Atrophic Acne Scars: The Role of Trifarotene as an Adjunct.

Acne vulgaris is a common, often chronic inflammatory disease that can affect all ages and skin tones. Beyond acute lesions, the sequelae of acne - specifically scarring and dyspigmentation - can be long-lasting, challenging to treat and have substantial psychosocial impact on affected individuals. For acne scarring, treatment modalities include topical, physical, and laser and light therapies, with combination approaches typically yielding optimal outcomes. Trifarotene is a novel fourth generation retinoid with targeted action towards retinoid acid receptor gamma (RAR-γ), the most common isotype found in the epidermis, that has previously been approved for the management of moderate-to-severe facial and truncal acne in individuals over the age of 12 years. Recently, data on trifarotene supports its application in acne scarring. Herein, we provide a succinct review on various treatments for acne scarring and explore how trifarotene and its mechanism of action present an additional topical approach to target atrophic acne scarring.

Endoplasmic reticulum stress as a target for retinoids in cancer treatment.

Retinoids, natural and synthetic derivatives of vitamin A, have various regulatory activities including controlling cellular proliferation, differentiation, and death. Furthermore, they have been used to treat specific cancers with satisfying results. Nevertheless, retinoids have yet to be converted into effective systemic therapies for the majority of tumor types. Regulation of unfolded protein response signaling, and persistent activation of endoplasmic reticulum stress (ER-stress) are promising treatment methods for cancer. The present article reviews the current understanding of how vitamin A and its derivatives may aid to cause ER-stress-activated apoptosis, as well as therapeutic options for exploiting ER-stress for achieving beneficial goal. The therapeutic use of some retinoids discussed in this article was related to decreased disease recurrence and improved therapeutic outcomes via ER-stress activation and promotion, indicating that retinoids may play an important role in cancer treatment and prevention. More research is needed to expand the use of vitamin A derivatives in cancer therapy, either alone or in combination with unfolded protein response inducers.

Common Skin Conditions in Children and Adolescents: Acne.

Acne is a chronic, recurrent inflammatory condition of the pilosebaceous unit. It affects approximately 85% of adolescents and creates significant psychosocial and financial burdens. The pathogenesis involves altered follicular growth and differentiation, microbial colonization with Cutibacterium acnes, increased sebum production influenced by androgen levels, and inflammation. Evidence-based risk factors include family history and body mass index. Diagnosis of acne is clinical, according to patient age and acne morphology and severity. Setting treatment expectations is an important aspect of management. For mild acne, benzoyl peroxide is an effective first-line drug as monotherapy or in combination with a topical retinoid and/or topical antibiotic. Oral tetracyclines are first-line drugs as part of a multipart treatment regimen for moderate to severe acne for patients older than 8 years. Oral isotretinoin is the first-line drug for moderate to severe inflammatory acne. Because of its teratogenic effects, its prescribing is monitored through the iPLEDGE Risk Evaluation and Mitigation Strategy (REMS) program. Prescribing oral or topical antibiotics as monotherapy for acne is not recommended, as this may increase microbial resistance. Combined oral contraceptives and spironolactone are used as adjunctive therapies in female adolescents. Patients with skin of color, pregnant patients, and transgender or gender diverse patients warrant special considerations in acne management.

Cutaneous Rosai-Dorfman disease: a systematic review and reappraisal of its treatment and prognosis.

Cutaneous Rosai Dorfman disease (CRDD) is a rare histiocytic disorder that shows distinctive clinical presentation and prognosis. Sufficient data is currently lacking regarding evidence-based management of CRDD. This systematic review aims to provide a comprehensive overview of CRDD, focusing on treatment approaches and outcomes. PubMed and Scopus databases were searched for studies on CRDD from June 1st, 2013 to May 31st, 2023. Articles describing cases of CRDD confirmed with histological examination were eligible for inclusion. All interventions for CRDD were analyzed. The primary outcome measure was the response of cutaneous lesions to treatment including complete response (CR), partial response (PR), and no response. The secondary outcome measures were mortality rate, relapse rate, and the occurrence of adverse events related to CRDD treatment. Eighty-seven articles describing 118 CRDD cases were included. The mean age was 48.2±16.8 years. The sex ratio (F/M) was 1.53. Nodular (46.6%) erythematous (45.3%) lesions, located on the face (38.1%) were the most prevalent presentations. Associated hematological malignancies were noted in 8 (6.8%) cases. Surgical excision was the most prevalent intervention (51 cases) with CR in 48 cases. Systemic corticosteroids were used in 32 cases with 20 CR/PR, retinoids in 10 cases with 4 CR/PR, thalidomide in 9 cases with 5 CR/PR, methotrexate in 8 cases with 7 CR/PR while observation was decided in 10 cases with 6 CR/PR. Factors independently associated with the absence of response to treatment were facial involvement (OR = 0.76, p = 0.014), and cutaneous lesion size (OR = 1.016, p = 0.03). This systematic review shows distinctive clinical characteristics of CRDD and provides insights into the appropriate management of the disease. It allowed a proposal of a treatment algorithm that should be interpreted in the context of current evidence and would help practitioners in treating this rare disease.

Unmet Needs in Darier's Disease from a Patient's Perspective: Lessons Learnt from the German Registry.

The MDHHgermany registry was initiated to characterize the "real-life" situation of affected individuals with Darier's disease (DD; Morbus Darier, MD) and Hailey-Hailey disease (HH), including their treatment and healthcare. To gain deeper insights into medical care of patients with DD, various aspects such as demographics, subjective symptoms, patient satisfaction with medical care, past and current therapies were explored. Patients with diagnosed DD were included. Subjective symptoms such as itch, pain and burning sensation were assessed. Individual therapy goals were recorded and patients assessed previous/current therapies along with satisfaction of medical care and treatment. A total of 55 patients were recruited; 47 patients were eligible for the analysis. Pruritus was rated the most bothersome symptom. Some 42.6% had not received systemic treatment so far or systemic therapies were rated ineffective (32.6%). Most commonly oral retinoids were prescribed, followed by corticosteroids. Patient satisfaction with medical care and treatment proved to be mediocre. This "real-life" data show an alarming unmet need regarding patients' satisfaction with medical care and treatment, evidenced by the reported lack of disease control. Further studies and interventions are needed to improve the spectrum of available therapies. MDHHgermany provides a foundational platform for future clinical trials, epidemiological studies, and pathophysiological analyses.

Synthetic retinoid-mediated preconditioning of cancer-associated fibroblasts and macrophages improves cancer response to immune checkpoint blockade.

BACKGROUND: The proliferation of cancer-associated fibroblasts (CAFs) hampers drug delivery and anti-tumor immunity, inducing tumor resistance to immune checkpoint blockade (ICB) therapy. However, it has remained a challenge to develop therapeutics that specifically target or modulate CAFs. METHODS: We investigated the involvement of Meflin+ cancer-restraining CAFs (rCAFs) in ICB efficacy in patients with clear cell renal cell carcinoma (ccRCC) and urothelial carcinoma (UC). We examined the effects of Am80 (a synthetic retinoid) administration on CAF phenotype, the tumor immune microenvironment, and ICB efficacy in cancer mouse models. RESULTS: High infiltration of Meflin+ CAFs correlated with ICB efficacy in patients with ccRCC and UC. Meflin+ CAF induction by Am80 administration improved ICB efficacy in the mouse models of cancer. Am80 exerted this effect when administered prior to, but not concomitant with, ICB therapy in wild-type but not Meflin-deficient mice. Am80-mediated induction of Meflin+ CAFs was associated with increases in antibody delivery and M1-like tumor-associated macrophage (TAM) infiltration. Finally, we showed the role of Chemerin produced from CAFs after Am80 administration in the induction of M1-like TAMs. CONCLUSION: Our data suggested that Am80 administration prior to ICB therapy increases the number of Meflin+ rCAFs and ICB efficacy by inducing changes in TAM phenotype.

Exploring Acne Treatments: From Pathophysiological Mechanisms to Emerging Therapies.

Acne vulgaris is a common dermatological condition that can present across different ages but predominantly affects adolescents and young adults. Characterized by various lesion types, the pathogenesis of acne is complex, involving genetic, hormonal, microbial, and inflammatory factors. This review comprehensively addresses current and emerging acne management strategies, emphasizing both topical and systemic treatments, procedural therapies, and dietary modifications. Key topical agents include retinoids, benzoyl peroxide, antibiotics, and other specialized compounds. Systemic options like antibiotics, hormonal therapies, and retinoids offer significant therapeutic benefits, particularly for moderate to severe cases. Procedural treatments such as laser devices, photodynamic therapy, chemical peels, and intralesional injections present viable alternatives for reducing acne symptoms and scarring. Emerging therapies focus on novel biologics, bacteriophages, probiotics, and peptides, providing promising future options. This review underscores the importance of personalized approaches to treatment due to the multifaceted nature of acne, highlighting the potential of innovative therapies for improving patient outcomes.

Milia en plaque on the shoulder as an early manifestations of mycosis fungoides.

Milia en plaque (MEP) is an uncommon skin condition identified as retroauricular confluent milium by Boulzer and Fouqet in 1903 [1]. It can be mistaken for other dermatoses like Favre-Racouchot nodular elastosis, steatocystoma multiplex, and nevus comedonicus. Milia en plaque can either be primary or secondary and is typically benign, often triggered by dermatological procedures like cryotherapy, as reported in this journal. In some cases, MEP can arise as a secondary manifestation of other diseases, including folliculotropic mycosis fungoides (FMF). Despite this association, there are few documented cases in the literature. Herein, we present a patient in whom MEP served as the initial clinical presentation of FMF; the treatment involved oral retinoids and phototherapy. Furthermore, we highlight distinctive features of both conditions. It is important to emphasize that early diagnosis and treatment of FMF are vital for the patient's quality of life. The presence of MEP can serve as a valuable indicator for identifying it.

IRX4204 Induces Senescence and Cell Death in HER2-positive Breast Cancer and Synergizes with Anti-HER2 Therapy.

PURPOSE: Rexinoids, agonists of nuclear retinoid X receptor (RXR), have been used for the treatment of cancers and are well tolerated in both animals and humans. However, the usefulness of rexinoids in treatment of breast cancer remains unknown. This study examines the efficacy of IRX4204, a highly specific rexinoid, in breast cancer cell lines and preclinical models to identify a biomarker for response and potential mechanism of action. EXPERIMENTAL DESIGN: IRX4204 effects on breast cancer cell growth and viability were determined using cell lines, syngeneic mouse models, and primary patient-derived xenograft (PDX) tumors. In vitro assays of cell cycle, apoptosis, senescence, and lipid metabolism were used to uncover a potential mechanism of action. Standard anti-HER2 therapies were screened in combination with IRX4204 on a panel of breast cancer cell lines to determine drug synergy. RESULTS: IRX4204 significantly inhibits the growth of HER2-positive breast cancer cell lines, including trastuzumab and lapatinib-resistant JIMT-1 and HCC1954. Treatment with IRX4204 reduced tumor growth rate in the MMTV-ErbB2 mouse and HER2-positive PDX model by 49% and 44%, respectively. Mechanistic studies revealed IRX4204 modulates lipid metabolism and induces senescence of HER2-positive cells. In addition, IRX4204 demonstrates additivity and synergy with HER2-targeted mAbs, tyrosine kinase inhibitors, and antibody-drug conjugates. CONCLUSIONS: These findings identify HER2 as a biomarker for IRX4204 treatment response and demonstrate a novel use of RXR agonists to synergize with current anti-HER2 therapies. Furthermore, our results suggest that RXR agonists can be useful for the treatment of anti-HER2 resistant and metastatic HER2-positive breast cancer.

Ripretinib inhibits HIV-1 transcription through modulation of PI3K-AKT-mTOR.

Despite the effectiveness of antiretroviral therapy (ART) in prolonging the lifespan of individuals infected with HIV-1, it does not offer a cure for acquired immunodeficiency syndrome (AIDS). The "block and lock" approach aims to maintain the provirus in a state of extended transcriptional arrest. By employing the "block and lock" strategy, researchers endeavor to impede disease progression by preventing viral rebound for an extended duration following patient stops receiving ART. The crux of this strategy lies in the utilization of latency-promoting agents (LPAs) that are suitable for impeding HIV-1 provirus transcription. However, previously documented LPAs exhibited limited efficacy in primary cells or samples obtained from patients, underscoring the significance of identifying novel LPAs that yield substantial outcomes. In this study, we performed high-throughput screening of FDA-approved compound library in the J-Lat A2 cell line to discover more efficacious LPAs. We discovered ripretinib being an LPA candidate, which was validated and observed to hinder proviral activation in cell models harboring latent infections, as well as CD4+ T cells derived from infected patients. We demonstrated that ripretinib effectively impeded proviral activation through inhibition of the PI3K-AKT-mTOR signaling pathway in the HIV-1 latent cells, thereby suppressing the opening states of cellular chromatin. The results of this research offer a promising drug candidate for the implementation of the "block and lock" strategy in the pursuit of an HIV-1 cure.

A review of the topical management of acne and its associated sequelae in the Asia-Pacific region with a spotlight on trifarotene.

Acne, a highly prevalent skin disease, can be particularly bothersome for patients of Asian background because of its impact on self-confidence and social interactions. In addition to active acne lesions, some patients may develop sequelae such as scarring, macular/postinflammatory hyperpigmentation, or erythema. The tendency of Asian skin to develop sequelae because of its increased susceptibility to irritation, cultural preferences for lighter skin phototypes, and differences in skincare regimens may all contribute to the increased burden of acne. Moreover, many Asia-Pacific countries do not have their own guidelines for acne management, and those that do often have no schedule in place for regular updates. In this article, we provide a critical review of the published guidance for the management of acne and its sequelae in the Asia-Pacific region, identifying gaps in current recommendations that could be addressed to enhance standards of acne care in Asia-Pacific countries. Along with highlighting the importance of a comprehensive skincare regimen to increase treatment efficacy and adherence, we discuss topical retinoids and retinoid combination options in the acne armamentarium that may be beneficial for sequelae prevention and management, such as adapalene 0.3% ± benzoyl peroxide 2.5%, tretinoin 0.05%, tazarotene 0.1%, and trifarotene 0.005%. In particular, trifarotene 0.005% has been observed to significantly reduce acne scar counts in a Phase 4 study. The recent data highlight the need to establish up-to-date guidance for acne and acne sequelae management in Asia-Pacific countries to provide optimal care to Asian patients.

[Clinical, therapeutic and pathophysiological aspects of Darier's disease]. / Aspects physiopathologiques cliniques et thérapeutiques de la maladie de Darier.

Darier Disease is a rare autosomal dominant inherited skin disorder classified as an acantholytic dermatosis. It manifests around puberty as brownish keratotic papules of skin folds and seborrheic areas, associated with onychopathy and mucosal involvementand have a chronic relapsing-remitting course with frequent exacerbations triggered by sun exposure, heat, friction, or infections. Darier patients have an increased risk of neuropsychiatric disorders, type 1 diabetes and heart failure. Short-term management relies on antibiotics/antiviral, topical corticosteroids and/or retinoids. Moisturizers, sun protection and avoiding triggers are essential for long-term management. Conventional long-term treatment is not standardized and many topical treatments, physical and surgical measures and systemic treatments are described in the literature.

La maladie de Darier est une génodermatose rare à transmission autosomique dominante. Elle se manifeste autour de la puberté par des papules kératosiques brunâtres des plis et des zones séborrhéiques, associées à une onychopathie et une atteinte muqueuse, et évolue par poussées déclenchées par les UV, la chaleur, les frottements ou les infections. Les patients atteints présentent un risque accru de diabète de type 1, d'insuffisance cardiaque et de troubles neuropsychiatriques. La prise en charge à court terme consiste en des antibiotiques/antiviraux, des corticostéroïdes topiques et/ou des rétinoïdes. Celle à long terme repose sur les émollients et l'éviction des facteurs déclenchants. Le traitement à long terme n'étant pas codifié, de nombreux traitements locaux et sytémiques, mesures physiques et chirurgicales sont décrits dans la littérature.

All-trans retinoic acid exhibits anti-proliferative and differentiating activity in Merkel cell carcinoma cells via retinoid pathway modulation.

BACKGROUND: The limited therapies available for treating Merkel cell carcinoma (MCC), a highly aggressive skin neoplasm, still pose clinical challenges, and novel treatments are required. Targeting retinoid signalling with retinoids, such as all-trans retinoic acid (ATRA), is a promising and clinically useful antitumor approach. ATRA drives tumour cell differentiation by modulating retinoid signalling, leading to anti-proliferative and pro-apoptotic effects. Although retinoid signalling is dysregulated in MCC, ATRA activity in this tumour is unknown. This study aimed to evaluate the impact of ATRA on the pathological phenotype of MCC cells. METHODS: The effect of ATRA was tested in various Merkel cell polyomavirus-positive and polyomavirus-negative MCC cell lines in terms of cell proliferation, viability, migration and clonogenic abilities. In addition, cell cycle, apoptosis/cell death and the retinoid gene signature were evaluated upon ATRA treatments. RESULTS: ATRA efficiently impaired MCC cell proliferation and viability in MCC cells. A strong effect in reducing cell migration and clonogenicity was determined in ATRA-treated cells. Moreover, ATRA resulted as strongly effective in arresting cell cycle and inducing apoptosis/cell death in all tested MCC cells. Enrichment analyses indicated that ATRA was effective in modulating the retinoid gene signature in MCC cells to promote cell differentiation pathways, which led to anti-proliferative and pro-apoptotic/cell death effects. CONCLUSIONS: These results underline the potential of retinoid-based therapy for MCC management and might open the way to novel experimental approaches with other retinoids and/or combinatorial treatments.

Treatment of plaque-psoriasis in HIV-positive patients.

Psoriasis is a chronic inflammatory disease that can often accompany human immunodeficiency virus (HIV) epidemics. Development of psoriasis in HIV patients is correlated with a decrease in CD4+ count. Significant variability in the clinical presentation of psoriasis makes it a challenging disease to diagnose. Furthermore, associated immunodeficiency complicates standard treatment with immunosuppressive and biological therapy. Articles that match the terms psoriasis and HIV were searched in MEDLINE and Embase and selected based on their relevance. Highly active antiretroviral therapy (HAART) is a medication regimen used to manage and treat HIV infection. In treating mild psoriasis in HIV-positive patients, topical agents combined with HAART are considered first-line therapy, followed by phototherapy. Second-line therapy includes oral retinoids, alone or combined. In treating challenging cases, apremilast has been used due to its lack of immunosuppressive effect. In case of progressive and refractory disease, limited data from studies suggest that immunosuppressive or biological therapy may be effective. Treatment of psoriasis in HIV patients remains a challenge, which is largely attributable to its complicated etiopathology and lack of an approved therapy option. In treating severe psoriasis, close collaboration with an infectious disease specialist is highly recommended. Further research is needed, preferably with an aim toward developing individualized therapy.

Self-reported clinical features and treatment effectiveness of Papillon-Lefèvre syndrome patients from five Latin American countries: A cross-sectional online survey study.

BACKGROUND/OBJECTIVES: Most studies about Papillon-Lefèvre syndrome (PLS) are limited to case reports and patients of the same nationality. This study aimed to determine the self-reported prevalence of signs, symptoms and treatment effectiveness in PLS patients from five Latin American countries. METHODS: An online survey was conducted among adult and paediatric patients from Mexico, Argentina, Colombia and Brazil. Data were collected using multiple-choice, open-ended and image-chooser questions on demographics, signs and symptoms, perceived treatment effectiveness and quality of life. RESULTS: Seventeen patients (10 males and 7 females) aged 4-47 years were surveyed. All had palmoplantar hyperkeratosis. Other affected sites were the feet and hand dorsum (82.35%), Achilles tendon (88.24%), forearms (58.82%), legs (29.41%) and glutes (23.53%). They frequently presented hyperhidrosis and nail pitting. Four had a history of delayed umbilical cord separation. All used topical treatments, with moderate effectiveness; half used oral retinoids, perceived as highly effective. Most reported decreased quality of life and walking difficulties. CONCLUSIONS: The study's results align with prior research on PLS, but reveal new insights, including the impact on patients' quality of life and a history of delayed umbilical cord separation. These findings warrant consideration in future research and patient care.

Dual role for microbial short-chain fatty acids in modifying SIV disease trajectory following anti-α4ß7 antibody administration.

BACKGROUND: Human Immunodeficiency Virus (HIV)/Simian Immunodeficiency Virus (SIV) infection is associated with significant gut damage, similar to that observed in patients with inflammatory bowel disease (IBD). This pathology includes loss of epithelial integrity, microbial translocation, dysbiosis, and resultant chronic immune activation. Additionally, the levels of all-trans-retinoic acid (atRA) are dramatically attenuated. Data on the therapeutic use of anti-α4ß7 antibodies has shown promise in patients with ulcerative colitis and Crohn's disease. Recent evidence has suggested that the microbiome and short-chain fatty acid (SCFA) metabolites it generates may be critical for anti-α4ß7 efficacy and maintaining intestinal homeostasis. MATERIALS AND METHODS: To determine whether the microbiome contributes to gut homeostasis after anti-α4ß7 antibody administered to SIV-infected rhesus macaques, faecal SCFA concentrations were determined, 16S rRNA sequencing was performed, plasma viral loads were determined, plasma retinoids were measured longitudinally, and gut retinoid synthesis/response gene expression was quantified. RESULTS: Our results suggest that anti-α4ß7 antibody facilitates the return of retinoid metabolism to baseline levels after SIV infection. Furthermore, faecal SCFAs were shown to be associated with retinoid synthesis gene expression and rebound viral loads after therapy interruption. CONCLUSIONS: Taken together, these data demonstrate the therapeutic advantages of anti-α4ß7 antibody administration during HIV/SIV infection and that the efficacy of anti-α4ß7 antibody may depend on microbiome composition and SCFA generation.