This study is an open, multicenter, non-randomized phase I clinical trial to evaluate the safety, tolerability, pharmacokinetics characteristics and preliminary efficacy of BL-M24D1 in patients with relapsed or refractory multiple myeloma and other hematologic malignancies.

The study is divided into two phases: a dose escalation phase (Phase Ia) and an expansion cohort phase (Phase Ib).

Inclusion Criteria:

1. Voluntarily sign the informed consent form and comply with the protocol requirements;
2. Gender is not restricted;
3. Age: ≥18 years and ≤75 years (Phase Ia); ≥18 years (Phase Ib);
4. Expected survival time ≥3 months;
5. Histologically and/or cytologically confirmed multiple myeloma or other hematologic malignancies that have failed standard treatment or for which no standard treatment currently exists;
6. Must have measurable indicators as defined by the protocol;
7. Physical condition score ECOG 0 or 1;
8. Toxicity from previous antitumor treatments has recovered to ≤ Grade 1 as defined by NCI-CTCAE v5.0;
9. No severe cardiac dysfunction, left ventricular ejection fraction ≥50%;
10. Organ function levels must meet the requirements;
11. Coagulation function: International Normalized Ratio (INR) ≤1.5, and activated partial thromboplastin time (APTT) ≤1.5 × ULN;
12. For premenopausal women with childbearing potential, a pregnancy test must be conducted within 7 days before starting treatment, the serum pregnancy test must be negative, and they must not be breastfeeding; all enrolled patients (regardless of gender) should adopt adequate barrier contraception throughout the treatment cycle and for 6 months after the end of treatment.

Exclusion Criteria:

1. Subjects with central nervous system involvement, etc.;
2. Use of chemotherapy, biologics, immunotherapy, etc., within 4 weeks prior to the first dose or within 5 half-lives;
3. History of severe heart disease;
4. QT interval prolongation, complete left bundle branch block, third-degree atrioventricular block;
5. Active autoimmune diseases and inflammatory diseases;
6. Diagnosis of other malignancies within 5 years prior to the first dose;
7. Hypertension poorly controlled by two antihypertensive medications;
8. Patients with poorly controlled blood glucose;
9. Unstable thrombotic events requiring therapeutic intervention within 6 months prior to the first dose;
10. Lung diseases defined as ≥ Grade 3 according to CTCAE v5.0; history of interstitial lung disease requiring hormone treatment, etc.;
11. Patients with peripheral neuropathy ≥ Grade 3 or persistent ≥ Grade 2 peripheral neuropathy with pain;
12. Patients with a history of allergy to recombinant humanized antibodies or human-mouse chimeric antibodies, or allergy to any excipient component of BL-M24D1;
13. Previous organ transplantation or allogeneic hematopoietic stem cell transplantation (Allo-HSCT);
14. Human immunodeficiency virus antibody positivity, active tuberculosis, active hepatitis B virus infection, or active hepatitis C virus infection;
15. Active infection requiring systemic treatment within 4 weeks prior to the first study drug administration, etc.;
16. Pleural, abdominal, pelvic, or pericardial effusion requiring drainage and/or accompanied by symptoms within 4 weeks prior to the first study drug administration;
17. Subjects with clinically significant bleeding or obvious bleeding tendency within 4 weeks prior to the first study drug administration;
18. Participation in another clinical trial within 4 weeks prior to the first dose;
19. Pregnant or breastfeeding women;
20. Patients who received live vaccines within 30 days prior to the first dose;
21. Other conditions deemed by the investigator as unsuitable for participation in this clinical trial.