The aim of the study is to assess the efficacy and safety of BCD-248 as a therapy for relapsing and/or refractory multiple myeloma.

Inclusion Criteria:

1. Signed informed consent form.
2. Age ≥18 years.
3. Documented diagnosis of multiple myeloma according to the IMWG criteria.
4. Measurable disease at screening.
5. Subjects who received at least 2 lines of therapy for multiple myeloma, including a proteasome inhibitor, an immunomodulatory drug, anti-CD38 therapy.
6. Documented progression according to the IMWG criteria during or after the last line of therapy.
7. Evidence of at least a partial response according to the IMWG criteria to at least 1 previous line of therapy.
8. ECOG score 0-2.

Exclusion Criteria:

1. Subjects who were previously treated with anti-BCMA or anti-CD3 drugs.

2. Use of any investigational medicinal products or medical devices within 30 days or 5 half-lives (whichever is longer) prior to the expected start of the study therapy or planned use of investigational medicinal products or medical devices during participation in this study, except for the use described in this Protocol.

3. Autologous hematopoietic stem cell transplantation within 12 weeks prior to the expected start of the study therapy or a history of allogenic stem cell transplantation, regardless of when it was performed.

4. Planned hematopoietic stem cell transplantation before disease progression during this study.

5. A history of other malignancies within 5 years before screening, excluding squamous and basal cell skin cancers, carcinoma in situ of the cervix or breast, or other malignancies, which, in the opinion of the Investigator, have been adequately treated and have a minimal risk of recurrence within 5 years.

6. Concomitant diseases and/or conditions that significantly increase the risk of AEs during the study:

   • Stable angina pectoris, functional class III-IV.
   • Unstable angina and/or myocardial infarction within less than 6 months before the expected start of the study therapy.
   • Chronic heart failure, NYHA class III-IV;
   • Clinically significant (in the Investigator's opinion) cardiac arrhythmia and conduction disorders that do not respond to the maximum possible antiarrhythmic therapy (therapy should be stable for 4 weeks before the expected start of the study therapy);
   • Moderate to severe asthma, grade III-IV chronic obstructive pulmonary disease, a history of angioedema, severe respiratory failure;
   • Active autoimmune diseases (subjects with type 1 diabetes mellitus and hypothyroidism requiring only hormone replacement therapy, as well as with skin diseases (vitiligo, alopecia, or psoriasis) that do not require systemic therapy are eligible);
   • Any infection within 14 days prior to the expected start of the study therapy, requiring systemic etiotropic therapy or which, in the opinion of the Investigator, may increase the risk of infectious complications;
   • Any other concomitant disease or condition, which, in the Investigator's opinion, significantly increases the risk of AEs in the study.

7. Subjects with amyloidosis.

8. Clinical signs of meningeal involvement of multiple myeloma.

9. HIV infection, active HBV infection, hepatitis C.

10. Major surgery within less than 14 days prior to the expected start of the study therapy, incomplete recovery from surgery, or planned surgery during participation in the study.

11. Pregnancy or breastfeeding, as well as intention to become pregnant or father a child during the study period and within 180 days after receiving the last dose of the IP.