AL amyloidosis begins in the bone marrow where abnormal proteins misfold and create free light chains that cannot be broken down. These free light chains bind together to form amyloid fibrils that build up in the extracellular space of organs, affecting the kidneys, heart, liver, spleen, nervous system and digestive tract.

The primary purpose of this study is to determine the recommended dose of CAEL-101 to facilitate progression of further clinical trials and evaluate safety and tolerability of CAEL-101 in combination with the standard of care (SoC) cyclophosphamide-bortezomib-dexamethasone (CyBorD) chemotherapy and daratumumab .

This is a multicenter, open-label, sequential cohort, dose-selection study of CAEL-101 in Mayo Stage I, Stage II and Stage IIIa AL amyloidosis patients. CAEL-101 will be administered in combination with the standard of care (SoC) cyclophosphamide-bortezomib-dexamethasone (CyBorD) chemotherapy and daratumumab.

The study is divided into two parts with the following objectives:

• Part A defines the safety and tolerability of CAEL-101 in combination with SoC CyBorD and determines the recommended Phase 3 dose (RP3D) of CAEL-101
• Part B evaluates the safety and tolerability of CAEL-101 in combination with SoC CyBorD and daratumumab

The study will also evaluate the pharmacokinetic profile of CAEL-101 and explore the PK profile of CAEL-101 when given bi-weekly (q2wk) versus once-monthly (q4wk) after the first 50 weeks.

Part A of the study will employ a 3+3 dose escalation design. At least 3 patients will be enrolled in each dose cohort unless adverse events (AE) preventing further dosing are observed. CAEL-101 will be administered in combination with the SoC CyBorD chemotherapy.

In Part B, a minimum of 6 new patients will receive CAEL-101 administered in combination with SoC CyBorD and daratumumab.

Patients from both Parts A and B will receive CAEL-101 therapy weekly and SoC throughout the safety observation period. CAEL-101 study drug infusions will continue, with dosing approximately every two weeks (q2wk) thereafter. SoC will continue per the Investigator's discretion. After completing approximately 50 weeks of treatment, participants may switch to an alternative maintenance dosing regimen of every four weeks (q4wk), if agreed upon by the Investigator and the Sponsor Medical Monitor.

Approximately 25 patients will be enrolled in the study at approximately 3 investigator sites.

Patients will be treated with CAEL-101 until death, unacceptable toxicity, symptomatic deterioration, Investigator decision, patient decision or Sponsor decision to terminate the study.

Key Inclusion Criteria:

Each patient must meet the following criteria to be enrolled in this study.

1. AL amyloidosis Mayo stage I, II or IIIa

2. For Part A only, measurable hematologic disease defined by at least one of the following:

   1. involved/uninvolved free light chain difference (dFLC) > 5mg/dL or
   2. free light chain (FLC) > 5mg/dL with abnormal Kappa/Lambda ratio or
   3. serum protein electrophoresis (SPEP) m- spike > 0.5 g/dL Patients with confirmed AL amyloid diagnosis without measurable disease may be enrolled with consultation and approval by the Sponsor Medical Monitor or their designee.

3. a. For Part A, currently on and continuing OR planned to start concurrent chemotherapy with CyBorD administered weekly as SoC. b. For Part B, currently on and continuing OR planned to start concurrent chemotherapy with CyBorD and daratumumab administered as SoC.

Key Exclusion Criteria:

Patients who meet any of the following criteria will not be permitted entry to the study.

1. Any form of secondary, hereditary, senile, localized, dialysis-related or leukocyte chemotactic factor 2-related (ALECT2) amyloidosis
2. Meets the International Myeloma Working Group (IMWG) definition of multiple myeloma. Patients with signs and/or symptoms attributable ONLY to amyloidosis and who do NOT meet IMWG definition of smoldering myeloma may be enrolled upon approval of the medical monitor.
3. Supine systolic blood pressure < 90 mmHg or symptomatic orthostatic hypotension, defined as a decrease in systolic blood pressure upon standing of > 20 mmHg despite medical management (e.g., midodrine, fludrocortisones) in the absence of volume depletion
4. Receiving dialysis
5. Myocardial infarction, uncontrolled angina, severe uncontrolled ventricular arrhythmias, or percutaneous cardiac intervention with recent stent, coronary artery bypass grafting or major cerebrovascular accident within 6 months prior to screening
6. Left ventricular ejection fraction (LVEF) < 45 percent by echocardiogram or multigated acquisition scan (MUGA)

Alexion has a public commitment to allow requests for access to study data and will be supplying a protocol, CSR, and plain language summaries.

Safety Set included all participants who were treated with at least 1 dose of CAEL-101.

First dose of study drug until 140 days after last dose of study drug (Maximum exposure: 38.90 months for Part A and 32.50 months for Part B)

Safety Set included all participants who were treated with at least 1 dose of CAEL-101. AE data were collected for the participants in the DLT period (Part A) by dose separately. Additionally, the AE data for participants in the DLT period were also collected regardless of dose level received along with the AE data collected during the Part A Continued Treatment (Part A) period as an Overall arm.