Inclusion Criteria:

• - Adults, age ≥ 18 and ≤ 65 years at the time of anticipated dosing (Day 1).

• - Healthy individuals without known current or chronic medical conditions, including no history of any autoimmune diseases, in the opinion of the Investigator.

• - Body mass index (BMI) ≥ 18 kg/m2 and ≤ 32 kg/m2.

• - Body weight ≥ 45and ≤ 100 kg.

• - Negative Coronavirus Disease 2019 (COVID-19) test within 24 hours prior to each dose.

• - Persons of child-bearing potential must have a negative pregnancy test and either abstain from sex or use highly effective method(s) of birth control from Day 1 through the duration of the study.

Exclusion Criteria:

• - Clinically significant findings in physical examination (PE), vital signs (blood pressure, heart rate, and body temperature), electrocardiogram (ECG), and safety laboratory parameters at Screening in the opinion of the Investigator.

• - Renal function calculated by the Chronic Kidney Disease-Epidemiology (CKD-EPI) equation with estimated glomerular filtration rate (eGFR) < 90 mL/min/1.73 m2 or abnormal level of proteinuria detected by dipstick at the time of Screening.

• - Any disease or condition that, in the opinion of the Investigator, might significantly compromise the cardiovascular, hematological, renal, hepatic, pulmonary (including chronic asthma), endocrine (e.g., diabetes), central nervous, or gastrointestinal (including an ulcer) systems.

• - Use of Anti-inflammatory OTC medications, e.g. acetaminophen and ibuprofen, taken within 1 week prior to and during the Screening period.

• - Receipt of an investigational drug within 28 days or 5 half-lives (whichever is longer) of the investigational drug(s) prior to Day 1.

• - Positive serology for human immunodeficiency virus (HIV) type 1 or 2, hepatitis (Hep) B surface antigen, or Hep C.

• - Positive test results for drug screen, including alcohol, at the time of Screening or on Day 1 prior to randomization.

• - Use of tobacco or nicotine-containing products more than the equivalent of 5 cigarettes/week within 30 days prior to (first) dosing.

Participants must abstain from nicotine use while inpatient.

• - History of receiving a live vaccine within 1 month of Screening.

• - History of splenectomy.

• - History of COVID or influenza vaccine within 2 weeks prior to Screening.

• - Planning to receive any vaccinations during the study period.

• - History of recurrent infections of uncertain cause.

This is a prospective, multi-center, randomized, double-blind, placebo-controlled, single ascending dose (SAD) and multiple ascending dose (MAD) study to evaluate the safety, pharmacokinetics (PK), and pharmacodynamics (PD) of MTX-101 in healthy adults (HA) and participants with celiac disease (CeD) and type 1 diabetes (T1D). This study will enroll HAs only in Part A and CeD and T1D patients only in Part B.

Arms

Placebo Comparator: Cohort A1S - Healthy Volunteers

Cohort A1S (n = 6): MTX-101, Dose level 1 IV or Placebo IV, Single dose

Placebo Comparator: Cohort A2S - Healthy Volunteers

Cohort A2S (n = 6): MTX-101, Dose Level 2 IV or Placebo IV, Single dose

Placebo Comparator: Cohort A3S - Healthy Vounteers

Cohort A3S (n = 6): MTX-101, Dose Level 3 IV or Placebo IV, single dose

Placebo Comparator: Cohort A4S - Healthy Volunteers

Cohort A4S (n =6): MTX-101, Dose Level 4 IV or Placebo IV, single dose

Placebo Comparator: Cohort A5Sa - Healthy Volunteers

Optional Cohort A5Sa (n = 6): MTX-101, Dose level 6 IV or Placebo IV, Single Dose

Placebo Comparator: Cohort A6M - Healthy Volunteers

Cohort A5M (n=8): MTX-101,Dose Level 4 IV or Placebo IV, dosed on Days 1 and 22 for a total of 2 doses

Placebo Comparator: Cohort A7M - Healthy Volunteers

Cohort A6M (n = 6): MTX-101, Dose Level 5 IV or Placebo IV, dosed on Days 1 and 22 for a total of 2 doses

Placebo Comparator: Cohort A7Ma - Healthy Volunteers

Optional Cohort A6Ma (n = 6): Dose Level 6 IV or Placebo IV, dosed on Days 1 and 22 for a total of 2 doses

Placebo Comparator: Cohort B8 - Celiac Disease or Type 1 Diabetes Patients

Dose Group 1 (n = 6): MTX-101 Dose Level 4 IV Day 1, placebo IV Day 22 Dose Group 2 (n = 6): Placebo IV Day 1, MTX-101 Dose Level 3 IV Day 22

Placebo Comparator: Cohort B9 -Celiac Disease or Type 1 Diabetes Patients

Dose Group 1 (n = 6): MTX-101 Dose Level 5 IV Day 1, placebo IV Day 22 Dose Group 2 (n = 6): Placebo IV Day 1, MTX-101 Dose Level 5 IV (or the maximum tolerated dose in Part A MAD) Day 22

Placebo Comparator: Cohort A5Sa -Healthy Volunteers

Optional Cohort A5Sa (n = 6): MTX-101, up to Dose Level 6 IV or Placebo IV, Single Dose

Interventions

Drug: - Placebo

Placebo

Drug: - MTX-101

MTX-101 (bispecific CD8 Treg modulator)