An Immunotherapy Vaccine (PIpepTolDC) for the Treatment of Patients With Type 1 Diabetes

Inclusion Criteria: * Willingness to undergo leukapheresis * Willingness to be followed for about 2 years post-prime dose * For participants who have a personal continuous glucose monitoring device (CGMD): Willingness to wear a second CGMD during mandated study CGMD visits * Diagnosis of type 1 diabetes based on American Diabetes Association (ADA) criteria * Historical presence of at least one type-1 diabetes associated autoantibody * GAD specific autoantibodies (glutamic acid decarboxylase autoantibodies \[GADA\]) * Islet cell cytoplasmic autoantibodies (ICA) * Islet-antigen 2 specific autoantibody (IA-2A) * Zinc transporter 8 specific autoantibody (ZNT8A); and/or * Insulin autoantibody (IAA) (must have been obtained within 7 days of initiating exogenous insulin replacement therapy) * Time from diagnosis to screening mixed meal tolerance test (MMTT) must be \>= 1 year but =\< 4 years * Stable glycemic control per participant's physician * HbA1c =\< 7.5% (=\< 58 mmol/mol) * Non-fasting C-peptide \> 0.017 nmol/L * Stimulated peak C-peptide levels \> 0.2 nmol/L from a 2-hour screening MMTT * Positive for \*04:01 allele, \*04:02 allele and/or \*04:04 allele at the human leukocyte antigen (HLA)-DRB1 gene locus * Does not possess the protective HLA-DRB1\*15:01-DQA1\*01:02-DQB1\*06:02 haplotype * Adequate self-assessment of blood glucose values and recording of glucose values, and administered insulin doses as deemed sufficient by the participant's physician * No diagnosis of type 1 diabetes related microvascular/macrovascular complications (e.g. nephropathy, retinopathy and neuropathy) * Deemed acceptable for autologous cell collection (i.e. leukapheresis) * Only for those who are naive to CGMD use: Deemed able to correctly use a CGM device following training session with a certified diabetes educator and manufacturer representative * Must meet organ function criteria Exclusion Criteria: * Other investigational agents, biologics * Anti-inflammatory therapy * Exception: Over-the-counter (OTC) anti-inflammatory agents (e.g. ibuprofen, Tylenol) are generally allowed. However, those requiring chronic OTC anti-inflammatory agents and unable to stop during mandated CGMD study visits will be excluded * Systemic corticosteroids within 28 days prior to leukapheresis * Systemic immunosuppressive therapy (e.g. cyclosporine-A, cyclophosphamide) * Monoclonal antibody therapy * Allergen immunotherapy within 28 days prior to leukapheresis * Vaccine(s) within 28 days prior to leukapheresis * Prior allogeneic organ transplant * Beta-cell stimulants (e.g. sulfonylureas such as glimepiride), glucagon-like peptide-1 agonists, dipeptidyl peptidase-IV inhibitors (exception: Those with acute exposure to these agents during T1D misdiagnosis may be permitted per PI discretion) * Insulin sensitizers (e.g. metformin, thiazolidinediones) within 2 months of leukapheresis * History of insulin sensitizer use (e.g. metformin, thiazolidinediones) ≥ 2 months * Other autoimmune/inflammatory disorders (exceptions: (i) Type 1 diabetes. (ii) Asymptomatic patients with incidental autoantibody titres may be permitted per PI discretion) * Other autoimmune/inflammatory disorders (exception type 1 diabetes) * Active infection requiring antibiotics and/or anti-virals * Known history of HIV, HBV, HCV, HTLV, syphilis * History of positive purified protein derivative (PPD) skin test * History of atopy requiring systemic treatment and/or history of severe allergic reactions * History or current malignancy * Unstable cardiac disease * History of vascular disease (e.g. deep vein thrombosis, stroke) * Clinically significant uncontrolled illness * Females only: pregnant or breastfeeding