XL Therapeutics is a biopharmaceutical company aiming to develop small molecule compounds to treat patients suffering from Wiskott-Aldrich syndrome (WAS) and X-linked thrombocytopenia, rare primary human immunodeficiencies caused by the absence or suboptimal function of the WAS protein (WASp), an adaptor protein expressed exclusively in hematopoietic cells and essential for normal hematopoietic cell function.