A Phase Ila trial titled Study of Fc-Optimized Anti-CD19 Antibody (MOR00208) to Treat Non-Hodgkin's Lymphoma (NHL) has completed recruitment. Specifically, a Phase I trial titled Safety and Tolerability of XmAb®5574 in Chronic Lymphocytic Leukemia, and a Phase Ila trial titled Study of Fc-Optimized Anti-CD19 Antibody (MOR00208) to treat B-cell Acute Lymphoblastic Leukemia (B-ALL) are completed. MOR00208 has or is currently being studied in clinical trials in CLL, ALL and NHL. MOR00208 has not been shown to mediate complement dependent cytotoxicity. The increase in binding of MOR00208 Fc to FcγR, due to XmAb engineered mutations, significantly enhances in-vitro antibody dependent cell-mediated cytotoxicity (ADCC), antibody dependent cell-mediated phagocytosis (ADCP), and direct cytotoxic effects (apoptosis) on tumor relative to the unmodified antibody. MOR00208 (previously named XmAb5574) is an Fc engineered humanized monoclonal antibody that binds CD19. The clinical development of CD19 directed antibodies had previously been limited by the internalization of the CD19 antigen, however, improved antibody modification technology has restored this potential therapeutic target. CD19 is an attractive target for cancers of lymphoid origin since it is highly expressed in nearly all chronic lymphocytic leukemia (CLL) and non-Hodgkin's lymphomas (NHL), as well as many other different types of leukemias, including acute lymphocytic leukemia (ALL) and hairy cell leukemia (HCL). The cytoplasmic tail of CD19 is physically associated with a family of tyrosine kinases that trigger downstream signaling pathways via the src-family of protein tyrosine kinases. It acts as a co-stimulatory molecule in conjunction with CD21 and CD81 and is critical for B cell responses to T-cell-dependent antigens. CD19 functions as a positive regulator of B cell receptor (BCR) signaling and is important for B cell activation and proliferation and in the development of humoral immune responses. It is B-lymphocyte lineage specific and not expressed on hematopoietic stem cells and other immune cells, except some follicular dendritic cells. The protein is a pan-B lymphocyte surface receptor and is ubiquitously expressed from the earliest stages of pre-B cell development onwards until it is down-regulated during terminal differentiation into plasma cells. BACKGROUNDĬD19 is a 95-kDa transmembrane glycoprotein of the immunoglobulin superfamily containing two extracellular immunoglobulin-like domains and an extensive cytoplasmic tail. The present disclosure is directed to identifying characteristics and biomarkers in patients that benefit from treatment with anti-CD19 antibodies. The present disclosure is also directed to a method for selecting a patient for treatment according to the above and to the use of an anti-CD19 antibody for the treatment of such a patient. The present disclosure is directed to a method of identifying a subject having chronic lymphocytic leukemia (CLL), non-Hodgkin's lymphoma (NHL), small lymphocytic lymphoma (SLL) or acute lymphoblastic leukemia (ALL) that is responsive to treatment with an anti-CD19 antibody, said method comprising: a) providing a blood sample obtained from said subject prior to treatment with said anti-CD19 antibody, b) determining the level of at least one biomarker in said sample selected from the group consisting of: i) peripheral NK cell count, and ii) CD16 expression levels on peripheral NK cells, c) comparing the level of said at least one biomarker in said sample to a predetermined cut off level, wherein levels of said at least one biomarker at or above the predetermined cut off level is indicative of a subject who would benefit from treatment with an anti-CD19 antibody.