1. A method for assessing (analyzing) the risk of possible side effects in a human patient due to the administration of the bispecific antibody CD19xCD3 to the specified patient, comprising determining the ratio of B cells to T cells in a sample of the specified patient, where a ratio of about 1: 5 or lower indicates the risk of side effects in the specified patient. 2. A method for treating malignant CD19-positive lymphocytes in a patient having a B: T cell ratio of about 1: 5 or lower, the method comprising: (a) administering a first dose of a bispecific antibody CD19xCD3 for a first period of time； and then (b) administering a second dose of said antibody for a second period of time； wherein said second dose exceeds said first dose. 3. A method for alleviating the course and / or preventing the occurrence of a side effect caused by the administration of a bispecific CD19xCD3 antibody to a human patient having a B: T cell ratio of about 1: 5 or lower, wherein the method comprises: (a) administering a first dose of said antibody for a first period of time and then (b) administering a second dose of said antibody for a second period of time； wherein said second dose exceeds said first dose. 4. The method of claim 2 or 3, wherein said human patient contains, or is suspected to contain, malignant CD19-positive lymphoma cells or leukemia cells. The method of claim 2 or 3, wherein the route of administration in step (a) and / or the route of administration in step (b) is intravenous. The method according to claim 3, wherein said side effect is characterized by a neurological reaction. The method according to claim 6, where the neurological reaction pre�1. Способ оценки (анализ) риска возникновения возможных побочных эффектов у пациента-человека, обусловленных введением биспецифичного антитела CD19xCD3 указанному пациенту, предусматривающий определение соотношения В-клеток к Т-клеткам в образце указанного пациента, где соотношение около 1:5 или ниже указывает на риск воз
