Answer:
There is no purely hypoallergenic dog. It is the proteins in the dander, urine and saliva that trigger the allergies. Dogs that shed a lot also leave hair around the house that hold some of the dander and keep it circulating in the air. So dogs that shed less may be better for those with allergies, such as Poodles. Standard poodles would be a good choice for a large breed that causes less problems with allergies. Another would be the Airedale terrier, the "King of the terriers".
Another, and larger breed, that is minimally shedding and generates less dander is the Bouvier de Flanders (originally popularized from Belgian cattle-herding dogs). Females of the breed typically run between 70 - 90 pounds, with males about ten pounds heavier; though males and even females over 100 pounds are not uncommon. They have a thick double-coat of hair instead of 'conventional dog fur,' consequently shed about as much as poodles. They don't share the dander issues found in Afghans, so they rank high on most lists of recommended hypoallergenic breeds.
Bouviers are wonderful family dogs, big and powerful, loyal and protective, but are willful and can be stubborn to train. Moreover, they will always try to herd. The breed has a strong prey instinct - strangely, more prevalent in females - and can be difficult around other animals. They need early socialization but will always require supervision. Though not necessarily 'outside' dogs, they do require reasonable daily exercise and love long runs or at least long walks. As might be expected, they are highly tolerant of cold weather. Frequent brushing is essential, as is cutting their coat three or four times a year. They need proximity to people but are decidedly not lap dogs; they like being nearby but don't enjoy constant 'fondling'.