Catheter-based devices and associated methods for immune system neuromodulation of human patients are disclosed herein. One aspect of the present technology is directed to methods of treating a human patient diagnosed with an immune system condition. The methods can include intravascularly positioning a neuromodulation catheter within a blood vessel proximate to neural fibers innervating an immune system organ of the patient. The method also includes reducing sympathetic neural activity in the patient by delivering energy to the neural fibers innervating the immune system organ via the neuromodulation catheter. Reducing sympathetic neural activity improves a measurable physiological parameter corresponding to the immune system condition of the patient.
