Immunotherapies aimed at preserving residual beta cell function in type 1 diabetes have been successful, although the effect has been limited, or raised safety concerns. Transient effects often observed may necessitate redosing to prolong the effect, although this is not always feasible or safe. Treatment with intralymphatic GAD-alum has been shown to be tolerable and safe in persons with type 1 diabetes and has shown significant efficacy to preserve C-peptide with associated clinical benefit in individuals with the human leukocyte antigen DR3DQ2 haplotype. To further explore the feasibility and advantages of redosing with intralymphatic GAD-alum, six participants who had previously received active treatment with intralymphatic GAD-alum and carried HLA DR3-DQ2 received one additional intralymphatic dose of 4 μg GAD-alum in the pilot trial DIAGNODE-B. The participants also received 2000 U/day vitamin D (Calciferol) supplementation for two months, starting one month prior to the GAD-alum injection. During the 12-month follow-up, residual beta cell function was estimated with Mixed-Meal Tolerance Tests, and clinical and immune responses were observed. C-peptide decreased minimally, and most patients showed stable HbA1c and IDAA1c. The mean % TIR increased while the mean daily insulin dose decreased at month 12 compared to the baseline. Redosing with GAD-alum seems to be safe and tolerable, and may prolong the disease modification elicited by the original GAD-alum treatment.