Flow cytometry-based diagnostic approach for inborn errors of immunity: experience from Algeria
Authors: Tahiat Azzeddine , Belbouab Reda , Yagoubi Abdelghani , Hakem Saliha , Fernini Faiza , Keddari Malika , Belhadj Hayet , Touri Souad , Aggoune Samira , Stoddard Jennifer , Niemela Julie , Zerifi Farida , Melzi Souhila , Aboura Rawda , Saad-Djaballah Amina , Ferhani Yacine , Ketfi Abdalbasset , Messaoudi Hassen , Bencharif Madani Tahar , Benhacine Zouleikha , Dehimi Abdelhak , Okka Kamelia , Amroune Fairouz , Fellahi Meriem , Bendahmane Chafa , Khoulani Radia , Oukil Asma , Soufane Asma , Bourelaf Imene , Boubidi Chahynez , Boukhenfouf Nadia , Amine Ifri Mohamed , Khelafi Noureddine , Boudiaf Houda , Khelifi Touhami Tahar , Meçabih Fethi , Boucelma Malika , Zelaci Amara , Gacem Ourida , Ladj Mohamed Samir , Mekki Azzedine , Bensaadi Nadia , Benhalima Malika , Zeroual Zoulikha , Bioud Belkacem , Benameur Mustapha , Bouhdjila Rachid , Bouzerar Zahir , Ibsaine Ouardia , Maouche Hachemi , Kedji Leila , Smati Leila , Boukari Rachida , Lambert Claude , Rosenzweig Sergio D. , Notarangelo Luigi D. , Djenouhat Kamel 
Published: July 2024

PurposeIn this study, we retrospectively reviewed the use of flow cytometry (FCM) in the diagnosis of inborn errors of immunity (IEIs) at a single center in Algeria. Sharing insights into our practical experience, we present FCM based diagnostic approaches adapted to different clinical scenarios.MethodsBetween May 2017 and February 2024, pediatric and adult patients presenting with clinical features suggestive of immunodeficiency were subjected to FCM evaluation, including lymphocyte subset analysis, detection of specific surface or intracellular proteins, and functional analysis of immune cells.ResultsOver a nearly seven-year period, our laboratory diagnosed a total of 670 patients (372 (55.5%) males and 298 (44.5%) females), distributed into 70 different IEIs belonging to 9 different categories of the International Union of Immunological Societies classification. FCM was used to diagnose and categorize IEI in 514 patients (76.7%). It provided direct diagnostic insights for IEIs such as severe combined immunodeficiency, Omenn syndrome, MHC class II deficiency, familial hemophagocytic lymphohistiocytosis, and CD55 deficiency. For certain IEIs, including hyper-IgE syndrome, STAT1-gain of function, autoimmune lymphoproliferative syndrome, and activated PI3K delta syndrome, FCM offered suggestive evidence, necessitating subsequent genetic testing for confirmation. Protein expression and functional assays played a crucial role in establishing definitive diagnoses for various disorders. To setup such diagnostic assays at high and reproducible quality, high level of expertise is required; in house reference values need to be determined and the parallel testing of healthy controls is highly recommended.ConclusionFlow cytometry has emerged as a highly valuable and cost-effective tool for diagnosing and studying most IEIs, particularly in low-income countries where access to genetic testing can be limited. FCM analysis could provide direct diagnostic insights for most common IEIs, offer clues to the underlying genetic defects, and/or aid in narrowing the list of putative genes to be analyzed.